The walk-off angle, interaction angle and refractive index are calculated with numerical methods under type I frequency-doubling phase-matching direction, while the fundamental frequency wavelength is 1064 nm in LBO crystal. The walk-off angle of the fundamental frequency wavelength is 0°~1.35°. The walk-off angle of the doubling frequency wavelength is 0°~1.52°. The interaction angle between fundamental frequency and doubling frequency waves is 0°~1.15°. The coupled wave equations and the conversion efficiency are numerical calculated considering the change of walk-off angle, the interaction angle and the refractive index. The results show that the conversion efficiency has maximum value (3.35%) when the phase matching direction is about (42.2°, 19°). In addition, the conversion efficiency is proportional to the square of the crystal length.