Abstract: Two time-domains blind adaptive estimation schemes were proposed based on OFDM systems. Both schemes improved the SLMS and had three advantages. First, the character of easy accomplish has been inherited from LMS. Second, the disadvantage of low speed has been solved. Finally, the estimation performance has been improved by combining adaptive variation step and adjusting strategy. Error curve and normalized mean square error curve are given in simulation, and shows that the modified SLMS and the time-variance step modified SLMS channel estimation schemes have faster converges comparing to the scheme based on SLMS, especially the latter one has better performances.