Based on the engine experiment, the transmission system of multi-purpose (rotary tilling, seeding, mowing and transporting) self-propelled pasture plot operation machine was optimally matched by using optimum design software which was developed in Matlab. The best matching scheme was obtained after simulation of power performance and fuel economy of transmission system and matching calculation between engine and transmission system. The selected matching scheme of engine and transmission system was optimized further, and then the transmission parameters were obtained after optimization. The results of transmission parameters were as follows: transmission ratio of first speed was 2.0039, second speed was 1.4595, third speed was 0.9775, fourth speed was 0.6751, reverse gear was 1.9840, transmission ratio of high-gear and low-gear were 1.0478 and 3.1102, respectively, and transmission ratio of central drive was 5.3711. Power performance and fuel economy of machine were improved to some extent, and matching degree between engine and transmission system was increased by 6.29% after optimization.