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-2.0cs 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.