In accordance with the requirements of agricultural production, the tractors and farm machinery should be combined into different units to conplete various farm operations. To obtain the optimum applied targets, the reasonable machinery regimentation should be made for the farm working units to realise the systematical coordination of machine structural characteristics and the performance.This paper standardized the theoretical calculation for the reasonable combination and provided a Turbo C computer program. The program can complete the reasonable combination of diferent machineries for three kinds of farm work,and more kinds of calculation can be done so long as a little modification is made in the program.