A fast testing instrument for vehicle lubricating oil quality is designed and implemented, which consists of PCB coaxial capacitance sensor and CMOS Schmidt flip-flop. The capacitance signal reflecting the change of lubricating oil quality is converted into frequency signal which is easy to measure. The frequency measurement is realized by STC89C2051 single chip microcomputer, and the quality of lubricating oil is indicated by LED indicator. The test results show that the tester is easy to carry, easy to operate and use, and can detect the different qualities of engine oil well, providing a scientific basis for the replacement of vehicle lubricants.