The invention discloses a tool and method for lowering the workpiece roughness under a low rotating speed turning work condition. The tool comprises a tool body, a tool bit and a connection piece. Thetool bit is connected with the tool body through the connection piece; a blade is arranged at the front end of the tool bit, and a cutting edge is arranged at the front end of the blade; and the width of the cutting edge is larger than the width of a to-be-machined workpiece. According to the tool and method for lowering the workpiece roughness under the low rotating speed turning work condition,the width of the cutting edge is larger than the width of the to-be-machined workpiece, the to-be-machined workpiece is completely covered by the cutting edge in the machining process, the surface roughness of the to-be-machined workpiece is lowered in a one-time cutting forming turning manner, application to workpiece machining under the low rotating speed turning work conditioner is achieved,and the workpiece surface quality is improved.