To investigate the variations in summer heat resources across Heilongjiang Province under the new climate state (1991-2020) and their impacts on the growth period and yield of cold-region rice, this study utilized 30-year datasets encompassing climatic observation records, rice phenological monitoring data, and yield statistics from 10 agro-meteorological experimental stations. Employing the linear trend rate method, linear regression analysis, and the Hodrick-Prescott (HP) filter, we analyzed the change characteristics of key thermal factors in summer, including ≥10℃ active accumulated temperature, mean temperature, and maximum/minimum temperatures, and their associations with rice phenological progression and yield components. The results showed that the summer heat resources in Heilongjiang Province from 1991 to 2020 had shown a significant upward trend. The tendency rate of active accumulated temperature of ≥10℃ was 36.89℃/10 a, and the increase in the minimum temperature was the largest, at 0.30℃/10 a. The increases in average temperature and maximum temperature were 0.15℃/10 a and 0.14℃/10 a respectively. From the perspective of the growing season dates, the heading date of rice showed a highly significant trend of advancing (with a tendency rate of -4.8 days per 10 years, P<0.01), while the milk-ripe stage and the maturity stage fluctuated relatively less. In terms of the length of the growing season, the heading stage, the milk stage and the reproductive growth period all showed a highly significant trend of extension (P<0.01). Over the past 30 years, the actual yield, trend yield, and meteorological yield of rice in Heilongjiang Province all exhibited a consistent increasing trend, with linear tendency rates of 804 kg per decade, 775 kg per decade, and 29 kg per decade, respectively. Among the thermal factors, mean temperature showed a highly significant correlation with the heading stage (P<0.01), while minimum temperature was highly significantly correlated with both the heading stage and milk-ripe stage (P<0.01). For every 1℃ increase in the mean temperature anomaly, the meteorological yield of rice increased by 110.87 kg per hectare. This study demonstrates that the enhancement of summer thermal resources under the new climate state (1991-2020) serves as the core climatic driver for the prolonged growth period and increased yield of cold-region rice. These findings provide a scientific basis for the efficient utilization of climatic resources and the optimization of variety distribution for cold-region rice cultivation.