The invention discloses a positioning tool for roller assembly. The positioning tool comprises a supporting seat, a machine frame assembly, a driving device and a transmission device, wherein the supporting seat comprises a base and a supporting wheel assembly, and the supporting wheel assembly comprises a first supporting wheel unit and a second supporting wheel unit; and the machine frame assembly comprises a driving side machine frame and an operation side machine frame, wherein the driving side machine frame and the operation side machine frame are connected through a cross beam unit, andthe driving side machine frame and the operation side machine frame which are parallel to each other and are symmetrically arranged are respectively supported on the first supporting wheel unit and the second supporting wheel unit in a rotatable mode, and are used for fixing a roller assembly from the two sides; and the transmission device comprises a chain wheel chain transmission mechanism and asynchronizing mechanism, the chain wheel chain transmission mechanism comprises a first chain wheel chain unit and a second chain wheel chain unit, the first chain wheel chain unit is used for the driving side machine frame, the second chain wheel chain unit is used for the operation side machine frame, one side of the synchronous mechanism is connected to the first chain wheel chain unit, and the other side of the synchronous mechanism is connected to the second chain wheel chain unit. The positioning tool not only can be applied to an eighteen-roller box structure, but also can be suitablefor other roller assembly or roller box structures.