A method of allocating a channel estimation number for a search space and a terminal device are provided. The method includes: reallocating, if a channel estimation number required for a target unit search space of a terminal device exceeds a first channel estimation number, the channel estimation number corresponding to the target unit search space, wherein, the first channel estimation number is a channel estimation number configured by a network-side device for the target unit search space or a maximum channel estimation number supported by the terminal device; a sum of second channel estimation numbers of the target unit search space after reallocating is less than or equal to the first channel estimation number.