Method for detecting water content in liquid under test by infrared ray which can instantly detect the water content of lubricating oil to improve the lubrication efficiency

The present invention is provided with an oil pipe, an infrared light emitter, an infrared light receiver and a processing part. The oil pipe circulates a liquid under test and is provided for the penetrated setting of the infrared light emitter and the infrared light receiver correspondingly. When the infrared light emitter emits an infrared light ranged between 900 nm and 902.5 nm. The infrared light penetrates through the liquid under test to reach the infrared light receiver. The processing part reads a voltage signal of the infrared light receiver according to a plurality of sampling time points to calculate a total value based on the plurality of voltage signals. It is then used to calculate an optical parameter of the liquid under test. Each optical parameter corresponds to a specific water content and the plurality of optical parameters constitute a basic data. The basic data is used to compare the optical parameter of the liquid under test with an unknown water content to obtain its water content. It