The present application relates to a terminal retainer, a connector housing, connector, and connector assembly. The terminal retainer has a tubular retaining part and the tubular retaining part comprises a tube wall and a cavity enclosed by the tube wall; the tubular retaining part axially extends a specified length; the tube wall is provided with a locking mechanism and the locking mechanism comprises an initial locking mechanism and a final locking mechanism which are respectively fitted with a mating mechanism to lock the terminal retainer in an initial locking position and a final locking position, respectively; the tube wall is further provided with an abutment mechanism, and the abutment mechanism is configured to abut against a snap-fit mechanism located in the cavity when the terminal retainer is in the final locking position so that the snap-fit mechanism can be retained in a snap-fit position. The terminal retainer may be preassembled with a connector housing to avoid scattering and loss of parts and to be ready for use.