Person-Organization Fit is conceptualized as three-factors fit-congruence of values and goals of Person and Organization, Demands-Abilities Fit and Needs-Supplies Fit. The necessary condition and sufficient condition of P-O Fit are discussed, and eight types of fit are deduced out in this paper. Linked with social exchange theory, the four better fits are developed into FitQuad, and the approaches to improve three less complete fits to full complete are explored. The conclusions of this research contribute to theories of P-O Fit and practice advices to organizations and employees on improving the situations of their P-O Fit.