This application provides a maximum power point tracking method and a device, to improve conversion efficiency of a control device in a photovoltaic power generation system, and reduce a loss of a power generation capacity. The method includes: adjusting, by the control device, an input voltage of the control device, where the input voltage is generated by one or more of the photovoltaic module and is transmitted to the control device; determining whether a difference between a first input power and a second input power of the control device is less than or equal to a setpoint, adjusting the input voltage of the control device according to the first input power and the second input power.