The phase matching angle and the non-collinear angle for ultrashort and mid-infrared optical parametric amplification (OPA) in MgO∶LiNbO3 are calculated. With pump light wavelength fixed at 800 nm, the non-collinear angle should be optimized between 1.74° and 2° when the seeded signal wavelength is 1053 nm, and the non -collinear angle should be optimized between 1.05° and 2.18° when the seed signal wavelength changes between 1046 and 1067 nm. Especially, when the seeded signal wavelength is 1057 nm and the non-collinear angle is 1.76°, the group velocities mismatching can be almost completely compensated with the pump light wavelength fixed at 800 nm. The series of signal light wavelength, mid-infrared light phase matching angle and non-collinear angle are also achieved when the group velocities are almost completely compensated with the pump light changing between 780 and 810 nm.