Real-time online monitoring of diesel engine oil viscosity is an important development direction of equipment condition monitoring and fault diagnosis. In practical applications, the real-time viscosity monitored online needs to be converted into the viscosity at the standard reference temperature of 100°C through the viscosity-temperature curve of the oil. And the viscosity of the oil The temperature curve changes dynamically with the oil pollution. In this paper, through experiments on the viscosity-temperature relationship of oil with different pollution degrees, the influence of oil pollution on the viscosity-temperature curve is analyzed, and a method to convert the real-time viscosity to the standard 100 A method of calculating the viscosity at the reference temperature in °C.