Dual-phase lamellar precipitates can be easily occurred in the austenitic steel valve in heat treatment and use. They affect seriously the performance of the valve at high-temperature, which is one important reason leading to valve failure. The morphology and precipitation location of lamellar precipitates of the 5Cr21Mn9Ni4N (21-4N) exhaust valve were investigated by scanning electron microscopy, and the influencing factors and precipitating mechanisms were analyzed. Experimental results show that, the lamellar precipitation is very sensitive to using or aging temperature, the higher temperature the more precipitates. The lamellar precipitation consists of continuous and discontinuous precipitation. The latter mainly appeared at the locations with larger deformation. Slip bands and deformation twins at high-temperature deformation and grain boundaries are important locations for precipitation.