Abstract: Mainly studied here in the essay are changes of the grain size and mechanical properties of the Φ711 mm×25 mm 316H steel pipe as affected by different heat treatment schedules. Also analyzed with the metallographic analysis are the relationship and variation regularities between the grain size and the heat treatment schedule. Finally it is concluded that the minimum grain size of the Φ711 mm×25 mm intermediate pipe that is cold-rolled, and then subjected to the heat treatment at 1 000℃+25 min is 7.5, based on which, the grain size of the Φ813 mm×15 mm finished pipe is well controlled within 6.0~6.5.