Traditional control methods has low control precision, and it is easy to cause that the actual power of the switch exceeds the power provided by the engine to some extent, this paper proposed a new method of engine switch control based on power tracking constraint. The maximum power in the process of engine switch control was determined. In order to facilitate the analysis of the following engine switch control, the power expression of switch branch was introduced. The power tracing constraint of a branch was built when other branches were disconnected. The power tracking constraint was transformed into the form which was suitable for engine switch control. Under the condition of power tracing constraint, the roll-channel of engine was considered as a double integral link. The engine starting time and running time were adjusted so as to achieve the same effect as the switch torque, and the switch control was realized. The improvement process of switch control was given under the condition that the controlled quantity was less than the setting value. Experimental result shows that the proposed method has high precision and good convergence, which can meet the requirements of engine for the switch.