Gravitational wave exploration won the 2017 Nobel prize in physics，which means that this probe is a major verification of Einstein's general relativity，and is also the key to open the new era of gravitational wave astronomy. Therefore，it is important for the teachers，students and general readers to have a knowledge of the theory of gravitational waves. In this paper，the theory about gravitational waves is given with general relativity. We introduce how to calculate the amplitude of gravitational waves for binary black holes which rotating with each other.We also introduce the relationship of chirp mass and the frequency of gravitational waves.