KDP crystal is grown by the traditional temperature lowering method. From the perspective of orientations, nonlinear refraction and nonlinear absorption for KDP crystal are performed by the single Z-scan method at the wavelength of 532 nm. Based on the application of the KDP crystal, the relationship between nonlinear optical parameters and direction has been proved in the picosecond laser pulse. Under the experimental conditions, it is shown that nonlinear refraction can be clearly observed, but no obvious nonlinear absorption phenomena. Self-focusing effect has been discovered in KDP crystal. Then, nonlinear refractive index γ（n2） and nonlinear susceptibility χ(3)k are calculated through the relative theory. The results show that the nonlinear optical parameters γ（n2）and χ(3)k for KDP crystals can be affected by orientations, and the values are small for phase-matching directions (I and II types).