Abstract: The relationships between the heating furnace time of casting slabs and the ultrasonic testing quality of hot-rolling medium plates were investigated. It is concluded that, (1) when the heating furnace time of 220 mm thickness casting slabs was less than 3 h, very bad ultrasonic testing quality of the plates would happen; (2) increasing the heating furnace time of the slabs could effectively improve the ultrasonic testing quality of the plates; (3) what caused the ultrasonic testing lost was micro-cracks in the pearlite band; (4) reducing the centerline segregation of the slabs could obviously improve the ultrasonic testing quality of the plates.