Abstract: An improved integer whitening filter search method for GPS ambiguity resolution on-the-fly is proposed. In the new method, the integer whitening filter is used to decorrelate the ambiguities. Then according to the decorrelated ambiguity covariance matrix and the transformed ambiguities float estimates, whether a search procedure is needed or not is judged. If yes, a conditional search is used to get the best ambiguity set; otherwise the transformed ambiguities can be fixxed just by rounding the float. The new method is simple and economical for GPS ambiguity resolution on-the-fly. It can be used to resolve ambiguity in only one epoch, too. Two numerical experiments are given to show the validity and availability of the new method.