This application provides a cell measurement method and terminal device. The cell measurement method includes: first determining, by a terminal device, whether a cell meets a first preset condition; and when the terminal device determines that the cell meets the first preset condition, measuring or evaluating, by the terminal device, the cell by using a first period; or when the terminal device determines that the cell does not meet the first preset condition, measuring or evaluating, by the terminal device, the cell by using a second period, where the cell being a serving cell or a neighboring cell of the terminal device corresponds to different first preset conditions, and the first period is different from the second period.