Abstract: The matching angle, the efficient nonlinear coefficient and the temporal and spatial walk-off length of collinear and non-collinear phase-matching for ultra-short mid-infrared laser optical parametric amplification in MgO:LiNbO3 crystal are analyzed. Based on this analysis, the group velocity matching, the efficient nonlinear coefficient’s increase and the larger signal’s walk-off length for non-collinear phase-matching optical parametric amplification are obtained. The enhanced spatial walk-off effect for the idler is also obtained, but it can be ignored. In a word, non-collinear phase-matching is beneficial to parametric conversion efficiency’s increase.