This paper introduces the concept of noise factor and noise operation, and constructs a noise group. We present a new perturbation algorithm for enhancing security of multivariate public key cryptosystems (MPKCs). European Consortium SFLASH which derives from Matsumoto-Imai scheme is a fast signature scheme intended for low cost smart cards. It was broken with the differential cryptanalysis by Dubois et al. in 2007. Taking Matsumoto-Imai system as an example, security analysis shows that the new algorithm can powerfully demolish its potential mathematical properties of the public key, and effectively avoid differential cryptanalysis without lowering the effciency of the original algorithm. This paper introduces the concept of noise factor and noise operation, and constructs a noise group. We present a new perturbation algorithm for enhancing security of multivariate public key cryptosystems (MPKCs). European Consortium SFLASH which derives from Matsumoto-Imai scheme is a fast signature It was broken with the differential cryptanalysis by Dubois et al. in 2007. Taking Matsumoto-Imai system as an example, security analysis shows that the new algorithm can powerfully demolish its potential mathematical properties of the public key , and effectively avoid differential cryptanalysis without lowering the effciency of the original algorithm.