An algorithm of digital modulation recognition based on instantaneous characteristic parameters is proposed for the application under low signal-to-noise ratio（SNR）.On one hand

the algorithm uses five relatively simple instantaneous characteristic parameters

which can improve the complexity of the algorithm and simplify the recognition process.On the other hand

a wavelet filter is designed to denoise instantaneous characteristic parameters

which can improve modulation identification ability a under low SNR.In addition

the algorithm directly recognizes signals in medium frequency

which is easy to compute and realize.Experimental results show that the recognition sucess rate is over 90% for different modulation signal when SNR is not lower than 5dB.