Abstract: The frequency of the radar signal parameters is important，which is useful for the target of screening，identification and classification.There are many digital frequency algorithms.They each have advantages and disadvantages.Generally，they can be divided into time domain frequency and frequency domain frequency.On the basis of the current digital frequency method，this paper for the first time applies the algorithm of subspace rotation unchanged to the study of passive radar frequency.In theory，this paper analyses the feasibility of the algorithm.The simulation proves the effectiveness of the algorithm.