In order to take into account the compatibility and interoperability of the future Global Navigation Satellite System (GNSS), and solve the problem of low resolution efficiency of multi-frequency, multi-mode and high-dimensional ambiguity in conventional methods, based on the lattice theory, a Closest Lattice Point (CLP) search algorithm was proposed to search the ambiguity integer value. First, the ambiguity search was transformed into the closest lattice point search problem of the known lattice points in the lattice. Then, according to the lattice base specification, the lattice base vectors with the minimum possible length and orthogonal to each other were obtained. Finally, the CLP search algorithm was used to search the optimal ambiguity parameters. The results of simulation and testing data verify that, the proposed CLP search algorithm is theoretically more efficient and reliable on the resolution of ambiguity parameters compared to the classical Least squares AMBiguity Decorrelation Adjustment (LAMBDA) and Modified LAMBDA (MLAMBDA) algorithms, and it has the search time of each parameter stable at 0.01 seconds, which means even in high-dimensional case, the CLP search algorithm is still stable and reliable.