In order to effectively and quickly identify the coding pattern of the enemy′s guidance laser and provide a longer time for our interference preparations, the principle and pattern of the finite-bit pseudo-random code are analyzed and the minimum period identification method of the bit pseudo-random code is proposed. The more phase subtraction method is used to solve the minimum integer ratio, which improves the computational efficiency. The simulation verification results show that the method can effectively identify the minimum period of the finite-bit pseudo-random code. When the number of received pulse signals is 4, the recognition probability is close to or exceeds 95%, and it has nothing to do with the number of bits of the shift register. And the effectiveness of the method is verified.