The invention relates to a detection method of the denial of service of public service numbers under a soft switching platform. The method comprises the following steps: 1. performing pre-judgment of the denial of service; 2. collecting the call data of the public service numbers to form a calling signal, performing Hilbert transform to the calling signal to obtain a calling analytic signal z(m) corresponding to a calling flow signal f(m), further calculating the instantaneous frequency W(m) of the calling flow signal f(m); and 3. performing variance analysis to the instantaneous frequency W1(m) of the detection window and the instantaneous frequency W2(m) of the history window to obtain variance bias coefficient sigma ration. The invention has the beneficial effect that the denial of service of public service numbers can be effectively detected under the soft switching platform. By combining the existing call data, the number of the attacker can be accurately determined.