In this paper, an approach for intra-pulse feature extraction of radar emitter signals is proposed based on wavelet transform. On the basis of the multi-resolution characteristics of wavelet transform, two energy entropies, as a two-dimensional feature vector to reveal the difference of radar modulation signals, are respectively extracted from approximation coefficient and multi-scale detail coefficients preserved through inter-scale correlations denoise in wavelet transform domain. In order to demonstrate the effectiveness and feasibility of the proposed approach, computer simulations indicates that the entropy features of ten typical radar emitter signals extracted by wavelet transform have good performance of clustering and suppressing noise when SNR is 0dB. In addition, proposed approach can separate the same modulation signals with different parameters.