The invention discloses a radar interference power allocation method for a radar and communication combination system. The method comprises the steps of firstly, acquiring frequency response of a target to a communication system, a radar signal and a communication transmitting signal according to prior knowledge; then, considering that echo of the communication transmitting signal reflected to a radar receiver by the target can be received and processed by a radar, taking the minimum total transmitting power of an onboard electronic interference system as a goal, establishing a radar interference power allocation model for the radar and communication combination system under the condition that the interference performance is satisfied, and solving the model via a Lagrange multiplier method; selecting interference power allocation J[k] absolute value 2 enabling the total interference power of the system to be minimum under the condition that the interference performance is satisfied as an optimal solution, bringing the optimal interference power allocation J[k] absolute value 2 of the interference system into the allocation model, thus obtaining the minimum total interference power satisfying the constraint condition. The method reduces the total transmitting power of the onboard electronic interference system, and improves the radio frequency stealth performance of the system.