In the problem of measuring cycle slip in receiver sustainable carrier phase, proposes an improved GPS cycle slip detection and repair method. Through analyzing reason of cycle slip, analyze the ionospheric residuals method, indicate its disadvantage, use carrier detection value linear fitting method for improvement of assistant detection, repair cycle slip, then use example for verification. The simulation results show that: the method can compensate the disadvantage of ionospheric residuals method, and it can effectively carry out detection and repair.