The rock mechanics, stress field, and fracture effectiveness significantly influence the generation, propagation, and production of fractures in tight sandstone reservoirs. However, variations in the mechanical properties of tight sandstones across different regions and incomplete evaluations of fracture effectiveness pose limitations to the scientific development of tight oil reservoirs. This study focuses on the Yanchang Formation's Chang 7 tight sandstone in the Ordos Basin's Longdong area. It delves into rock mechanics, covering rock density, compressive strength, friction coefficient, and brittleness index. Through strain differential analysis and drilling-induced fracture identification, the stress magnitude and orientation were determined: average maximum horizontal stress at 36.30 MPa, average minimum horizontal stress at 30.20 MPa, and average vertical stress at 45.49 MPa, with the primary horizontal stress oriented close to the east-west direction. These data contribute to predicting fracture characteristics during hydraulic fracturing. Additionally, the study assesses the effectiveness of natural fractures and employs Coulomb failure criteria to analyze the conditions for transforming ineffective fractures into effective ones: when internal fracture pressure reaches critical sliding pressure, ineffective fractures transform into effective ones. The average critical sliding pressure for fracture sliding is 30.11 MPa, with an average critical pressure gradient of 0.0179 MPa/m. These research results help to clarify the distribution characteristics of reservoir fractures and the conditions for their effectiveness transformation, providing more targeted tight oil development strategies for the eastern Longnan region.