The invention discloses a locating clamp plate for an engine cam shaft and an eccentric shaft rear end slot locating clamp plate and an assembly method, belonging to the field of engine assembly. The locating clamp plate comprises an intake cam shaft rear end slot locating clamp plate, an exhaust cam shaft rear end slot locating clamp plate and an eccentric shaft rear end slot locating clamp plate. The intake cam shaft rear end slot locating clamp plate, the exhaust cam shaft rear end slot locating clamp plate and the eccentric shaft rear end slot locating clamp plate are located on three different horizontal planes, the inside end part of the intake cam shaft rear end slot locating clamp plate is provided with a clamping part A, the inside end part of the eccentric shaft rear end slot locating clamp plate is provided with a clamping part B, and the inside end part of the exhaust cam shaft rear end slot locating clamp plate is provided with a clamping part C. The embodiment of the invention has the advantages of convenient use and accurate location by designing the locating clamp plate into three parts on three different horizontal planes for locating an intake cam shaft, an exhaust cam shaft and an eccentric shaft; and the accuracy of engine timing phase is high.