A dustproof precise powder paving mechanism for a metal 3D printer comprises a speed reducer, a transmission component, a powder paving fixing plate and a sliding component; the powder paving fixing plate is located above a powder feeding table, the speed reducer is connected to the transmission component and has a shell, and first dustproof pieces are arranged around the shell; the sliding component comprises a sliding block and a guide rail, the guide rail is arranged on a base, the sliding block slidably sleeves the guide rail, and one end of the powder paving fixing plate is fixed on the sliding block; the transmission component has a synchronous belt, one end of the powder paving fixing plate is connected to the synchronous belt, and the transmission component drives the sliding block to slide in a reciprocating manner along the guide rail. The first dustproof pieces are arranged around the shell, dust is prevented from falling into the speed reducer, influence on the work of important and precise parts is avoided, the service life of the powder paving mechanism is favorably prolonged, and operation stability of the powder paving mechanism is improved.