The invention discloses a multi-constellation GNSS fusion high-precision dynamic positioning method under complex environmental conditions. The method comprises the following steps of step1, acquiringa floating point ambiguity solution set b<^> and a variance-covariance matrix Qb<^>, decomposing the b<^> and the Qb<^> and acquiring a whole cycle ambiguity value, if the whole cycle ambiguity valuesatisfies a setting requirement, entering into a step4, otherwise, entering into a step2; step2, removing the ambiguity of an ith satellite from the b<^>, then carrying out ambiguity decomposition, and acquiring the distance sni between a Ratio value ratioi and a floating point ambiguity, and an optimal whole cycle ambiguity; step3, grouping the ratioi and the sni according to a setting thresholdvalue, and then determining an optimal ambiguity subset, and according to the optimal ambiguity subset, carrying out whole cycle ambiguity calculation and acquiring a whole cycle ambiguity value; andstep4, according to the whole cycle ambiguity value, carrying out GNSS fixed solution calculation, and acquiring a GNSS dynamic positioning result. In the invention, the influence of the floating point ambiguity with a large deviation on ambiguity decomposition can be effectively avoided, the ambiguity can be rapidly fixed, and the correctness and the reliability of a GNSS positioning result areensured.