A detection tool of a SCR system diagnostic device comprises a voltage adjustable output module as load modules, a resistance adjustable module, a short circuit module, a power module, a first CAN communication module, a first interface and an MCU controller, wherein the voltage adjustable output module, the resistance adjustable module, the short circuit module, the power module, the first CAN communication module and the first interface are all connected to the MCU controller; the voltage adjustable output module, the resistance adjustable module, the short circuit module, the power module and the first CAN communication module are all connected to the first interface; and the first interface has a plurality of pins corresponding to respective load modules to form detection channels corresponding to respective load modules. The detection tool can efficiently and automatically achieve detection, saves detection time and manpower input, can achieve batch detection, has high detection precision, covers various working conditions, avoids misjudgment caused by human factors, and eliminates the influence of early failed components on equipment.