Abstract: In this paper, we study the echo cancellation technology of the on-frequency digital repeater. By analyzing the convergence condition of adaptive filter based on least mean square(LMS) principle, we find that existing adaptive filtering algorithm using delay to eliminate the relevance is not able to guarantee the convergence condition being satisfied in principle, even when the outer channel is a single-path or a main path of multipath channel.We propose a novel algorithm sending the signal into the adaptive estimator after a delaying time to solve the problem. The novel algorithm conditionally improves the effect of echo cancellation. Further more, this paper proposes three new principles to eliminate the multipath echo.