Abstract: We first study the Poisson equation $\Delta u =f$ on complete noncompact Riemannian manifolds by constructing solutions with precise growth estimates. In particular we established the necessary and sufficient conditions on when the equation admits a solution of logarithmic growth when the base manifold $M$ has nonnegative Ricci curvature. Then we applied the result to the study of plurisubharmonic functions on complete Kahler manifolds. Combining with $L^2$ estimate on the power of the canonical (anti-canonical) holomorphic line bundle over $M$ we can obtain some optimal curvature decay results on complete Kahler manifolds with nonnegative Ricci curvature. In the last part of the paper we also study the complete Kahler manifold with pinched curvature using the solution of Poincare-Lelong equation we constructed. This is a joint work with Y Shi (Peking) and L-F Tam (Hong Kong).