A computer controlled magnetic particle brake simulated loading system was developed for agricultural machinery experiments.The loading system included a computer,a PC-6313 interface card,a loading installation and a measuring installation. The system programme was designed with Turbo C and assembly language.A proportional feed back control method was used to improve the accuracy of the loading system. Operation was easy,using a Chinese characer menu as interface surface.Test results showed that the loading system could be used as a general-purpose tool in agricultural machinery experiments.