With the improvement of industrial modern technology and the surge of labor costs, industrial production and assembly enterprises improve efficiency and ensure quality while saving production, manufacturing and labor costs. as a result, automatic production and assembly lines are gradually replacing manual operation and inefficient production transfer. The on-line measuring instrument is designed on the basis of automatic assembly line. first of all, it is composed of measuring mechanism, frame or bottom plate, pressing mechanism, measuring mechanism, servo drive mechanism and positioning mechanism. it is erected above the turntable of the automatic assembly line, and when the positioning mechanism of the workpiece being placed on the base plate is transmitted to the turntable with the automatic assembly line. The PLC program controls the lifting of the rotary disc cylinder, the servo drive of the upper compression mechanism and the measuring mechanism moves down successively, and several groups of data can be transferred to the computer at one time. The computer judges whether the product is qualified according to the set parameters, and finally the cylinder lift drops, the compression and measuring mechanism are reset under the operation of servo drive, and the qualified products are transmitted normally with the assembly line. The defective products enter another assembly line with the rotation of the turntable at one angle, and the whole testing process is completed.