The edge crack cause of 309L austenitic stainless steel plate in the hot rolling is analyzed by means of metallographic structure observation and thermodynamic calculation. Results test show that the hot rolling temperature of steel plate 309L (0.012% C

0.034% N) is at 1 260℃：and large area of continuous reticular δ ferrite exists in the triangle area of slab edge. In the subsequent heating process

the ferrite content increased continuously to up 24%

which lead to the decrease of plasticity and formation o£ edge crack in rolling process. By controlling 0.015% ~ 0.025% C

and 0.04% ~ 0.05% N in steel

and slab heating at 1 150 ℃

the ferrite content in steel decreases to 10.7% to be available to avoid the edge crack of 309L steel plate and coil qualified rate up to 100%.