PDC bit is applicable to drill in soft to medium-hard homogeneous layer with high ROP and long service life, but not suitable for drilling in gravel and multi-interbedded formation. According to the problems of low efficient, short service life and low core recovery in coal-measures soft and hard multi-interbeded formation(3~8 degree), the paper put forward a design with strengthening radius retention structure, improving the water circulation and advancing auxiliary cutting teeth. φ77mm PDC bit was designed and manufactured, and good application effect was achieved in the exploration borehole No.3 of Tonghua coal mine in Qijiang County of Chongqing.