Online bypass automatic sampling detection of oil particle contamination, moisture content, viscosity, density, abrasive particles, dielectric constant, oil temperature and other indicators in the oil tank or pipeline. The detection results are compared with the set standards, and an alarm is given if they exceed the standard. Typical applications: thermal power plant turbine oil station, EH oil station, fan lubricating oil station, online monitoring of oil quality of military, ship, machinery and chemical equipment.