The extraction of pitch period has a wide range of applications in the field of speech signal processing. Inspired by traditional autocorrelation algorithm and the pitch detection method that used in Multi-Band Excitation (MBE) vocoder, we have put forward an improved algorithm for pitch period extraction. This algorithm has five parts: Pre-process, pitch rough estimation in time domain, pitch smoothing, search with Time Variable Filter, decimal pitch estimation. Experimental results show that this new algorithm can achieve higher accuracy and compared with traditional autocorrelation algorithm, this approach owns a better noise immunity.