On the basis of the methods of pseudopotential and large unit cell the research of deep lev- els of point and cluster defects in ZnGeP2 (ZGP) was carried out. It was shown that owing to lowering of the crystal lattice symmetry localised states of point defects in the ternary compound essentially differ from such states in its binary analogue GaP. Small quasicubic antisite defects clusters reduce the value of band gap, but render weak influence on the probability of optical transitions. But both single and the cluster antisite defects cause large modifications in deep levels of another point defects closed to them. On an example of phosphorus vacancy it was shown that intensive optical transitions with small energies can appear and cause an absorption in near IR – range because of antisite defects effect.