The crystal chemical behavior of zinc in bioapatite is different from that in geological body, thus the traditional theory of apatite isomorphism substitution is not completely applicable to the Ca site substitution in bioapatite. In order to explain the appearance of zinc in bioapatite, the authors made a review on the existence of zinc and the mechanism of zinc substitution for Ca site and the influence of zinc substitution in this paper. The implications of crystal chemistry of zinc in bioapatite on the diagnosis and treatment of human tumors were also discussed. Both theoretical and experimental results show that zinc incorporation into bioapatite can take place by occupying the Ca2 vacancy of the defect complex and the local structure would shrink as a whole. The substitution of zinc would have a great impact on crystallite dimension, crystallinity, cell parameters and so on. When zinc is fixed in the lattice of pathological calcification associated with human tumors, it might affect the zinc content in surrounding tissues and body fluids, thus affecting the metabolism of zinc in human body.