In order to improve the speed ratio control accuracy and stability of Continuously Variable Transmissions (CVTs), the thrust balance impact factors were studied and the relationship between the primary pulley thrust and the secondary pulley thrust was analyzed. Theoretical analysis and experiment verification methods were utilized. A math model for thrust ratio was developed. The impact on balance thrust ratio from speed ratio, torque ratio, input torque and primary speed was investigated in test bench experiment. The results are as follows: 1) the balance thrust is proportional to the ratio between the primary and secondary working wrap angles; 2) The thrust ratio becomes smaller when the input torque is larger under the same speed ratio condition; 3) The thrust ratio increases when the input torque ratio becomes larger; 4) The thrust becomes smaller when the maximum input torque becomes larger under the same torque ratio condition; 5) The impact from primary speed can be ignored. This paper explains the balance mechanism of thrust ratio and provides a theoretical and experimental basis for controlling speed ratio accurately.