In order to explore the influence of cement mixing pile spacing on the pile bearing performance, the cement mixing pile disposal project of K1+435 ~ K1+550 section located at Yuzhuan 1st road in Chongqing is taken as the background, theoretical research and numerical simulation are combined, and the lateral friction resistance, vertical stress and settlement changes of reinforcement area under different pile spacing conditions are discussed and analyzed. The results show that: 1) The neutral point of the lateral friction resistance of the cement mixing pile appears at the length of 1/4 pile of the buried depth, and the position of the neutral point moves down with the increase of the pile spacing; 2) The peak value of the negative friction resistance on the pile side increases from 15.7 kPa to 18.3 kPa when the pile spacing increases from 3 times the pile diameter to 5 times the pile diameter, which is increased by 16.6%; 3) The vertical stress of the cement mixing pile decreases along the buried depth direction, and when the pile spacing increases, the stress level at the top of the bearing layer continues to increase, and the settlement of the surface and reinforcement area increases with the increase of pile spacing; 4) The bearing capacity of the composite subgrade of the cement mixing pile with a pile spacing of 3.3 times the pile diameter is 456.68 kPa, and the disposal effect is good. The results can provide certain references for the application of cement mixing piles in weak composite subgrade treatment projects.