For technology of super-resolution direction finding, in order to avoid effect on the result of Direction of arrival (DOA) when number of signals is estimated by error, a kind of two-dimensional (2-D) DOA estimation algorithm based on projection decomposition is proposed in this paper. First, maximal possible number of signal is assumed, then we use MUSIC algorithm to estimate the primary angles of them, at last, true DOA are acquired with projection decomposition coefficient by getting rid of fake angle values. The performance of the method is better than MUSIC algorithm under the circumstance of knowing number of signals when signal to noise ratio(SNR) is low, the computing time is not obviously increased, and it is adapt to any plane array, computer simulation results prove the effective of the method.