Abstract: Dispersive formulas were deduced adding a phase correction term to the optical path difference, and the formulas were validated through ray tracing method. From both the ray tracing method and formulas, the stretcher model with Offner triplet stretcher were studied. The influences of the incident angle and the distance between the grating and the concave mirror were discussed. The residual dispersions of Offner triplet stretchers and a conjugate compressor systems of some grating-concave-mirror distances and incident angles were analyzed comparatively. The influences of unmatched gratings on dispersions were also presented.