In this paper, an analytical pulse stretcher model for the single-grating stretcher based on ray-tracing is presented. By this model, the effect of misalignment of optical element of stretcher on the second dispersion and on the deviation angle of the output pulse is analyzed. When the misalignment angle for the plane reflective mirror M1 is 0.2 degree, the second order dispersion of the stretcher reaches the maximum. Increasing or decreasing misalignment angle, the second order dispersion of the stretcher decreases. That indicates that the misalignment of optical element of stretcher increases deviation angle of output pulse. The finite size of the diffraction grating and the concave mirror in the stretcher has constrain effect on spectrum bandwidth. A new way of increasing second order dispersion by misaligning reflective mirror, and improving bandwidth by increasing size of the diffraction grating and the concave mirror in the stretcher is proposed. It is important to the design of the stretcher.