In order to develop a new type of precision spraying equipment, a set of variable-rate spray system based on electric control valve device as a converter was developed, and the step response characteristics of the system were studied by using experimental methods. The result shows that the maximum rise time is 1 s in the condition of step amplitude ΔQ=0.4, 1.4, 3.4, 3.9, 4.4L/min, which is comparable with variable-rate spray system controlled by changing flow press; the rise time, peak time and overshoot show correlation with the amplitude, which indicates that the system belongs to nonlinear system. So the control design of this type of variable-rate continuous spray system must take nonlinear problems into account.