With the aid of a VM4100 high temperature viscometer and DM2000 high temperature densimeter, the viscosity measurement platform of heat transfer oil has been established, with the highest experimental temperature being 350 ℃. The measurement of viscosity values of standard heat conducting oil samples T66 and S750 and their mixed liquids in different temperature ranges thus can be achieved. The errors of viscosity measurement of standard thermal conductive oil samples of T66 and S750 are 4.55% and 3.90%, each less than 5%, which indicates that a VM4100 high temperature viscometer can be applied for the engineering measurement of thermal conductive oil viscosity. A regression analysis has been made of the measured viscosity value of the standard heat transfer oil sample, with the calculation error of the viscosity-temperature relationship being less than 9%. The relatively high calculation accuracy indicates that the formula can be used to predict the viscosity of heat transfer oil within high temperature range, and the experiment verifies the fact that the viscosity of the heat transfer oil mixture can be calculated by weight according to the mass composition.