A power control method in a communications system, the communications system including a network device, a first terminal and a second terminal; the power control method comprising: sending, by the second terminal path loss indication information to the network device, wherein the path loss indication information is used to indicate a path loss between the second terminal and the first terminal; receiving, by the first terminal, first power indication information determined and sent by the network device, wherein the first power indication information is determined by the network device based on a first power value and the path loss between the second terminal and the first terminal, and the network device determines the first power value based on quality information that is of the channel for communication between the second terminal and the first terminal, that is obtained by the second terminal through measurement, and that is sent by the second terminal to the network device, and wherein the quality information of the channel comprises at least one of the following: a receive interference level, signal received quality, and received signal strength; determining, by the first terminal, a transmission power of the first terminal based on the first power indication information; and transmitting, by the first terminal, a signal to the second terminal based on the transmission power; wherein before the receiving, by the first terminal, the first power indication information sent by the network device, the method further comprises: sending, by the first terminal, a first signal to the second terminal, wherein the first signal is used by the second terminal to determine the path loss between the first terminal and the second terminal based on a transmit power of the first signal; wherein the transmit power of the first signal is a preset fixed power value, or is indicated by using first-signal transmit power indication information sent by the first terminal to the second terminal, or is configured by the second terminal or the network device, or is pre-configured. sending, by the second terminal path loss indication information to the network device, wherein the path loss indication information is used to indicate a path loss between the second terminal and the first terminal; receiving, by the first terminal, first power indication information determined and sent by the network device, wherein the first power indication information is determined by the network device based on a first power value and the path loss between the second terminal and the first terminal, and the network device determines the first power value based on quality information that is of the channel for communication between the second terminal and the first terminal, that is obtained by the second terminal through measurement, and that is sent by the second terminal to the network device, and wherein the quality information of the channel comprises at least one of the following: a receive interference level, signal received quality, and received signal strength; determining, by the first terminal, a transmission power of the first terminal based on the first power indication information; and transmitting, by the first terminal, a signal to the second terminal based on the transmission power; wherein before the receiving, by the first terminal, the first power indication information sent by the network device, the method further comprises: sending, by the first terminal, a first signal to the second terminal, wherein the first signal is used by the second terminal to determine the path loss between the first terminal and the second terminal based on a transmit power of the first signal; wherein the transmit power of the first signal is a preset fixed power value, or is indicated by using first-signal transmit power indication information sent by the first terminal to the second terminal, or is configured by the second terminal or the network device, or is pre-configured. sending, by the first terminal, a first signal to the second terminal, wherein the first signal is used by the second terminal to determine the path loss between the first terminal and the second terminal based on a transmit power of the first signal; wherein the transmit power of the first signal is a preset fixed power value, or is indicated by using first-signal transmit power indication information sent by the first terminal to the second terminal, or is configured by the second terminal or the network device, or is pre-configured.