Disclosed is a relative orientation angle calculation method comprising steps of obtaining inertial sensor data of first and second mobile devices, the first mobile device being capable of sending a first signal to the second mobile device; obtaining a sending frequency that the first signal has when the first mobile device sends the first signal to the second mobile device; obtaining a receipt frequency that the first signal has when the second mobile device receives the first signal sent from the first mobile device, the first signal receiving influence of the Doppler effect in a sending process in which the first signal is sent to the second mobile device from the first mobile device; and calculating, based on the inertial sensor data, the sending frequency, and the receipt frequency, a relative orientation angle between the first and second mobile devices.