At first under the external magnetic field H acting around the axes (x,y,z) of lattice field was the calculation of the splitting of energy level of the Cr³⁺in K₃[Cr(CN)₆] shown. Secondly, the simultaneous calculating method for the energy level and the wave function was shown under the external magnetic field H acting around the axes (a,b,c) of cryatal. It is called the simultaneous calculating method by us, that the values of energy level and wave function calculated out at the same time by the computer. The calculating process is reduced and the amount of work is decreased. And this method ensures that the perpendicular and unitary conditions of the obtained wave-function can be satisfied. This method may° be extended to the calculation of other similar-question. Finally,the values of wave function and the energy level diagrams are obtained by this method.