The invention discloses a dynamic characteristic testing method of a transfer function of a nuclear instrument control system. The method comprises the following steps: step I: designing and constructing a testing environment, and connecting a signal generator, the instrument control system and a waveform recorder; step II: allowing the signal generator to input a step signal to the instrument control system, outputting an analog signal after operation of the instrument control system, and allowing the waveform recorder to acquire input and output signal waveforms and form a waveform data file; step III: performing waveform data processing according to the output waveform data file, and calculating a transfer function parameter; step IV: recording algorithm step response output steady-state values, the calculated transfer function parameter and a waveform trend of output signals of the algorithm step response output steady-state values according to the waveform data processed result; and step V: comprehensively determining the correctness according to an output value after stable step response, the waveform trend of the output signals and the calculated transfer function parameter. The method is low in overall testing workload and implementation cost.