The pulse expansion and deformation caused by group velocity dispersion in optical parametric effect of the negative uniaxial crystal CsLiB6O10 are studied, by momentum conservation and coupling wave equations. The numerical results show that, under the conditions of hyperbola secant wave form, no chirp modulation, pulse width of 50 fs and crystal length of 10 nm, the pulse expansion caused by group velocity dispersion for incident wavelength of 532 nm is 1.6 times of that for wavelength of 213 nm. The pulse expansion is related to the incident light wavelength and crystal length, and the pulse expansion and deformation are more severe for shorter wavelength and crystal length. The wave form symmetry is destroyed and the side band phenomena is also introduced by the pulse expansion.