A wavelet transformation based detection method is proposed for the voltage collapse occurring under the transmission limit， in which no effective detection methods are used up to now. The abnormal phenomenon induced by the voltage collapse can be detected quickly with the help of applying wavelet transformation on voltages of load nodes and the main diagonal of inverse of dynamic Jacobian matrix（sensitivity）. The proposed method can point out the first bus that experiences voltage collapse. Effectiveness of this method is proved by the simulation on IEEE 39-bus testing system with motor as part of its load.