A method of multi-level authentication based on two-beam interference is proposed. By verifying the "password" and "phase key" of one user simultaneously, the system can thus achieve the two-factor authentication on the user's identity. This scheme can not only check the legality of one user, but also verify his identity level as an authorized user and then grant the user the corresponding permissions to access the system resources. While operating the authentication process, which largely depends on an optical setup based on interference, a "phase key" and a password-controlled "phase lock" are firstly loaded on two spatial light modulators (SLMs), separately. Then two coherent beams are respectively, modulated by the two SLMs and then interfere with each other, leading to an interference pattern in the output plane. It is recorded and transmitted to the computer to finish the last step of the authentication process: comparing the interference pattern with the standard verification images in the database of the system to verify whether it is an authorized user. When it turns to the system designing process for a user, which involves an iterative algorithm to acquire an estimated solution of an inverse problem, we need to determine the "phase key" according to a modified phase retrieval iterative algorithm under the condition of an arbitrarily given "phase lock" and a previously determined identity level (corresponding to a certain standard verification image). The theoretical analysis and simulation experiments both validate the feasibility and effectiveness of the proposed scheme.