In this paper, the dynamic characteristic of the buried crescent InGaAsP/Inp laser is analysed by the computer simulation method. The dependences of the threshold current and the single model cut-off condition on the structure parameters such as the active layer thickness (centre) d0, the channel width W, the cavity length L, the stripe width s, and the material resistance Rx are obtained.Based on the simulation analysis, the approximate expression between the structure parameters and the threshold current is provided. From this, the laser physical characteristic can be estimated simply and directly, and the model of injection carrier Gaussian profile is also propounded. Using this model, the current spreading and the gain profile were correctly calculated, and a series of analytical expressions about the maximum gain gmax, the threshold current density Jth, the mode gain Gth, the optimal active layer thickness d0,min and the optimal threshold current density Jth,min ate derived. According to the analysis mentioned above, the optimal design parameters for this type of laser are obtained as follows:d0= 0.15-0.2 μm, W = 2-4 μm, L = 200 μm and s= 10-15μm.