Embodiments of the present invention propose a D2D communications method, apparatus, and system. In the solution, a D2D SPS available period in which a first terminal is capable of using a D2D SPS resource is greater than one SC period. Therefore, in the D2D SPS available period, the first terminal needs to determine the D2D SPS resource only one time, and a second terminal also needs to decode SCI only one time to determine the D2D SPS resource. In this way, the first terminal does not need to determine a D2D SPS resource in each SC period, and the second terminal also does not need to decode SCI in each SC period to determine the D2D SPS resource. Therefore, D2D communication efficiency is improved.