To explore the rule of stress increment in unbonded tendons and design method of moment redistribution, the finite element was modeled by ABAQUS soft-ware for unbonded prestressed concrete flat plates. The plates were divided into the column strips and the middle ones. Stress increment in tendons and moment redistribution coefficient of unbonded prestressed concrete flat plates were studied, which are influenced by the combined reinforcement index and grade of non-prestressing reinforcement. It is shown that the stress increment in tendons increases at the serviceability and ultimate limit states and moment redistribution coefficient in critical section of support reduces with the higher yield strength of non-prestressing reinforcements in flat plates. Then expressions of stress increment in tendons and moment redistribution coefficient in prestressed concrete flat plates were developed, in which the combined reinforcement index and grade of non-prestressing reinforcement were considered.