The present invention provides an ambiguity fixing method. According to the ambiguity fixing method of the invention, ambiguity sets are sequenced according to the ascending sorting result of the height angles of all satellites; if the sequenced ambiguity sets fail to pass ratio check, dimension reduction processing is performed on the sequenced ambiguity sets; the updated ambiguity sets which have been subjected to the dimension reduction processing are adopted as the new search targets of the LAMBDA method; and therefore, a search range can be narrowed. Since the dimension reduction processing is based on the height angles of the satellites, and therefore, influence on the quality of observation values caused by the complexity of an observation environment can be decreased, and the success rate of the fixing of ambiguities is improved; if the updated ambiguity sets which have been subjected to the dimension reduction processing are adopted as the new search targets of the LAMBDA method, and the fixed salutations of the ambiguities cannot be obtained still, the observation values of satellites of which the continuous tracking time length is short are eliminated according to the continuous tracking time length of the satellites, and therefore, a phenomenon that the ambiguities cannot be fixed caused by the instability of newly-emerging satellite observation values can be avoided effectively, and the success rate of the fixing of the ambiguities can be further improved.