Abstract: During the application of P.C. members, the service behavior is ineluctable to be affected by some factors. Based on the theoretical analysis of prestress enhancement on flexural stiffness of a P.C. member, further considerations and analysis of actual influences caused by friction loss, creep and shrinkage were taken. Effects in the corresponding circumstances had been analyzed and commented. After considerate discussion for the typical results on flexural stiffness, instructional usage was pointed out, which could be used as a reference to evaluate the practical performance of P.C. members for designer and constructor.