Elaborate theory analysis has been done for the modulation characteristics of semiconductor 1aser and analytical expression has been deduced through the research of rate equation of semiconductor 1aser. By using the general regression neural network, a neural network model of the modulation characteristics of semiconductor laser is developed. Then, the modulation characteristics of semiconductor laser are analyzed and a semiconductor 1aser is designed through the trained neural network model. The simulation results are well agreed with the theoretical analysis results. Furthermore, this method has the advantages of high speed, high accuracy, good repeatability, etc. The results of research show that the characteristics of semiconductor laser can be analyzed and the some dimensions of semiconductor laser structure can be obtained using the neural network model.