The utility model discloses a printer carriage unit horizontal left-right movement guide mechanism, which comprises a word frame, wherein a guide shaft is movably run through the lower portion of a word frame, a guide rail which is parallel to the guide shaft is arranged above the guide shaft, a locking clamp and a guide wheel which are respectively arranged on the front and the rear sides of the guide rail are arranged on the upper portion of the word frame, the middle portion of the locking clamp is hinged with the word frame, a spring which enables the locking clamp to rotate around a hinged position and press the guide wheel is arranged between the lower portion of the locking clamp and the work frame, and the locking clamp which is hinged on the word frame in the middle portion applies a force which enables the lower portion of the locking clamp to depart away form the word frame to the lower portion of the locking clamp through the spring which is arranged between the lower portion of the locking clamp and the word frame. The upper portion of the locking clamp can rotate around the hinged position and press toward the guide wheel according to lever principle, thereby enabling the guide rail which is arranged between the guide wheel and the locking clamp to be clamped, guaranteeing a carriage unit to be clung to the guide rail during the horizontal left-right movement process, and contributing to improve printing quality of a printer.