The invention discloses a D2D communication downlink resource sharing method enhancing cellular network security. Under the limiting condition of ensuring secure communication of a cellular user, the rate of a D2D user is optimized by jointly optimizing a transmitting power of the cellular user, a transmitting power of a D2D link and cellular channel allocation. When the channel allocation is given, the method delivers an optimal cellular user transmitting power and an optimal D2D link transmitting power, and further provides a cellular channel allocation algorithm. An independent pre-estimated power of each channel is optimized according to the channel information, so as to acquire a joint, optimized power control and channel allocation solution. The method has the advantages of being low in complexity, small in calculating amount and easy to implement.