The slabs produced by new No.3 castes at Baosteel are mainly used for heavy plates, the size of which is 220,250,300 mm×（12002300） mm with 2000 mm is a dominant one. Internal and surface quality of slabs is good, except some longitudinal cracks were observed in some cracksensitive peritectic slabs with the thickness of 220 mm. A kind of mold powder for cracksensitive heavy plate steel was developed, which has high basicity, high crystallization rate and low viscosity. High crystallization rate increases the heat resistance of slag film, which makes slab cool mildly in mold, so the longitudinalcrackrate of slab is decreased. Suitable lubrication can be obtained by use of low viscosity mold powder to ensure smooth casting process.