The invention discloses a simulator of the main generator of a diesel locomotive. A serial communication circuit used for ISP in the simulator of the main generator of the diesel locomotive sends nominal parameters and boundary parameters of the main generator to a single chip through serial communication, the single chip collects field current signal of the main generator input by an analog quantity input circuit; and the output voltage and the current of the main generator are calculated by the mathematical model of the interior main generator thereof according to the diesel rotate speed signals and locomotive speed signals input by a frequency quantity input circuit, a digital quantity input circuit and locomotive condition signal, and output to a analog quantity output circuit. The device adequately simulates output voltages and currents of the main generator under various working conditions and load changing conditions, so that a control system of microcomputer controls the main generator of the diesel locomotive as well as the main generator is controlled on a locomotive. The invention has the advantages that the ground experiment can be realized before loading, the main generator is not required to be directly controlled, the cost is saved, and the device is economical and practical.