This study employs data from the CGSS and utilizes OLS regression and RDD to examine the impact of political identity and north-south differences on social trust. The main contributions of this study are as follows. First, the analysis finds that political outlook has a significant and positive effect on social trust, and this effect remains robust across different models, suggesting that Party membership may enhance individual social trust through political identification. Second, this study verifies the systematic north-south disparity in social trust levels whose result is same as previous research. Finally, by employing the Qinling-Huaihe Line as a natural experimental cutoff and implementing the RDD method providing stronger causal evidence demonstrating the important influence of geographic factors on social trust, as trust levels decline with increasing latitude. Overall, this study explores the key determinants of social trust in China from the dual perspectives of political identity and regional culture.