The principle restoration of Zhang Heng's Seismoscope and the realization of its seismic detection function are crucial for the seismological community to recognize and accept Zhang Heng's Seismoscope as a scientific instrument. Pillar and Copper-instrument are the two most critical information in historical literature records. The Pillar must support the Copper-instrument, and the Copper-instrument must be placed on the top of the Pillar, otherwise it cannot be called Pillar; Understanding this relationship of support and positioning leads to the emergence of the principle model of the Seismoscope. The "secondary structure excitation model of primary-secondary structure resonance system" is proposed as the principle model of the Seismoscope. By utilizing the resonance amplification effect of the primary-secondary structures (at least 5.0 times), and the lever amplification effect of the trigger mechanism (at least 4.0 times), a relative displacement amplification of at least 20 times for most seismic motions is achieved, with some amplifications exceeding 50 times. Theoretically, this enables the effective excitation of Zhang Heng's Seismoscope under microseisms (imperceptible to humans). Coupled with an automatic locking system, the Seismoscope achieves an automatic seismic detection function. The primary structure (Ground-Motion) can be simplified as a "cantilever structure with a large concentrated mass at the top and supported at the bottom on a horizontal elastic foundation." The secondary structure (Wind-Observation) consists of 8 pendulums corresponding to 8 directions. Each pendulum is suspended using a "pin", and the pendulum rod is made of copper, serving as a tension-compression rod. This design ensures that the pendulum's swing direction is essentially perpendicular to the axis direction of the pin, allowing for the detection of seismic motion direction. The seismic motion direction measured by the Seismoscope is the one caused by microseisms that initially excites the secondary structure to undergo a significant displacement relative to the primary structure. If the direction aligns with the earthquake-source direction, it may be possible to measure the earthquake-source direction. Due to the significant differences in stiffness and mass between the primary and secondary structures, they can be separated and calculated separately as small-damping ideal linear elastic single-degree-of-freedom systems. The relative displacement of the secondary structure given by this simplified method is slightly smaller than the precise calculation results of the ANSYS finite element model, with a deviation of no more than 10%, indicating that the simplified method has high accuracy and credibility. The relative displacement amplification coefficient of the secondary structure is the primary indicator for whether the seismograph is easy to be excited. The relative displacement amplification coefficient spectrum of the secondary structure is proposed as the basic technical diagram for designing the Seismoscope. A statistical analysis was conducted on the calculation results of 18 sets of far-field seismic records. If requiring the relative displacement amplification coefficient of the secondary structure to be no less than 5.0, it is preliminarily believed that the optimal natural vibration period of the primary-secondary structures ranges from 2.1 s to 2.6 s. The on-site installation and adjusting process to control the natural vibration period range of the primary-secondary structures of the Seismoscope for achieving resonance effects is provided. Further field tests are required to verify its seismic detection function. The principle restoration and instrument design of Zhang Heng's Seismoscope have been preliminarily achieved. Using modern seismic observation results and structural dynamic analysis technology, the principle model of the Seismoscope proposed in this paper conforms to historical records and can achieve the (micro-)seismic detection function