The invention provides a blade grinding device which is accurate in positioning and automatically adaptable to a blade. The blade grinding device comprises the blade, a grinding wheel assembly, a blade clamp assembly and a transmission assembly. A blade grinding line which acts on the whole grinding work needs to be adjusted and positioned in the earlier stage; manual preparation in the earlier stage is completed after the blade is positioned onto the blade clamp assembly; the blade clamp assembly and the grinding wheel assembly abut against each other automatically, so that a grinding position is determined. Different blades are clamped, fixed and positioned through a specially-made clamp, the positioning precision and the grinding precision can be further promoted, and thus the advantages of completing grinding simply through one-time feeding and improving the working efficiency are achieved.