The indicating instrument is the key part of the equipment, The accuracy of the indicating instrument plays an important role in judging the technical condition of the equipment, preventing fault occurs in time and repairing faulty equipment quickly. In order to solve the problem that the indicating instrument Accuracy of a certain type of equipment can be Checked at Original location, an Checking instrument is designed. The Checking instrument takes AT89C52 microcomputer as the control core, and uses assembly language programming, A/D and D/A conversion and digital tube display etc technology to realize the automatic test of equipment power voltage and the automatic Check of Accuracy of equipment"s temperature gauge, pressure gauge, current/voltage gauge, tachometers, pressure loss gauge. introduces AT89C52 microcomputer,TCL1549 and TCL5617 chip. The Circuits about digital tube display, operation keys, power voltage test, temperature gauge Check, current/voltage gauge Check and their working principle are given. The flow charts of the main program, function selection program, function confirmation program and temperature gauge Check program are given, as well as the assembly language main program. After the analysis and verification of the experimental data, the Check results are correct, and the practical application meets the requirements of use and maintenance, with remarkable effects.