To improve the performance of hydraulic transmission system, a study on the matching performance of engine and hydraulic torque converter was conducted. According to the power split-flow form, hydraulic transmission systems were divided into two classical structure modals. With the two structure modals were abstracted according to graph theory, a computer program was developed using Python language, which could finish auto-derivation and auto-solving, and finish the matching calculation of engine and torque converter. Combined with a matching calculation example, a comparison study of the results of the two structure modals under different road conditions was carried out, which showed that the matching performance of engine and hydraulic torque converter in the hydraulic transmission systems with front power split-flow was obviously influenced by external load, and the load effect had to be considered in the study on its cooperating performance.