This paper introduces a new arc envelop truing method of metal-bonded diamond grinding. It utilizes the arc profile of rotary cone-shaped truer, namely electrode, to envelop wheel profile during Electro-Contact Discharge (ECD) truing. The aim is to realize precision truing of diamond grinding wheel profile for grinding of hard-brittle material. The arc envelope truing principle of wheel profile was analyzed by the use of 3D spatial geometry to identify lean angle of the truer. Then the arc envelop truing and grinding experiments were carried out to investigate truing precision and ground surface in comparison with straight truing and GC stick truing. It was confirmed that the arc envelope truing can obtain sub-micro truing precision of metal-bonded diamond grinding wheel at the depth of cut of micro degree. It may improve greatly form accuracy and ground surface.