Beam quality (BQ) of the coherent beam combination system of lasers in two-dimensional distribution is studied with BQ as the evaluation factor for beam quality of the output laser. By using passive phase locking technology with optical feedback in a ring cavity, the experimental setup of coherent beam combination of four lasers in two dimensions is built, and the combination of four fiber lasers is realized. When the diameter of ideal beam is selected as the circumscribed circle diameter of sub-beams in near-field, circular flat-topped beam or Gaussian beam is taken as the ideal beam model. Corresponding to different bucket sizes of laser spot in far-field, BQs are measured separately. The results show that, the selection of ideal beam model in the definition has little effect on BQ, but the selection of bucket size of laser spot in far-field has greater impact on BQ. The BQs of different coherent beam combination systems should be evaluated with a clear definition of BQ.