The distribution of laser beam power on all ranks of transverse mode is proposed to evaluate laser beam quality, and the fundamental mode is proposed to evaluate low ranks laser beam, against the weakness of other beam quality factors, and the measuring method is studied.The beam spot images captured by a CCD detector are input into a nonlinear network which bases on the Hopfield network principle, the dynamics steady state is obtained by computing the energy function of the network, and the proportion of all ranks of transverse mode in the steady state is just the measurement result. During the experiment, a diode-pumped solid-state laser was used to emit laser beams, and the captured beam spot images were input into the nonlinear network after image processing, and the whole process only cost a 2.4G CPU 15s, and the proportion of fundamental mode was 69%. The results were used to compose a new spot digital image, the relative error between which and the input image was 3.53%.The beam quality factors proposed in this paper can meet the needs of laser beam evaluation in a laser designing, maintenacing and checking. The nonlinear network with CCD bulilt in this paper can measure structure parameter precisely, and it will play a important role in project application.