According to the working environment of the polar glacier core drilling,a separatory funnel capillary viscometer which can be used for testing the viscosity of liquids under ultra-low temperature conditions was designed. This viscometer has a simple structure and it is easy to operate,which can meet the testing requirements of different temperature conditions.The viscosity of the dimethyl silicone oil KF-96L-2.Ocs was measured under different temperatures using this designed viscometer,and it is found that the viscometer coefficient K changes linearly with temperature.This testing method has relatively high test accuracy and its relative error is less than 4%,which can be used to test the viscosity of the different liquids in ultra-low temperature conditions.