According to application of thermal insulation materials in the practical construction of electrical heat tracing in viscous oil pipeline, impact factors of rigid polyurethane foam widely used as new insulation material are systemically analyzed by Grey Relational Analysis (GRA) in the theory of Grey System to find out priorities among those factors. To further study their performances and to improve the quality of constructions, ten field experiments were carried out in Tanggula Mountain. The foaming conditions and the performances of the rigid polyurethane foam were recorded to be analyzed by GRA. The analysis results, acting as scientific guidance for construction, show that the insulation quality of rigid polyurethane foam is mainly determined by the ratio of components, thus the priority is to control such dominant factor and overall consideration of other factors should be taken to ensure insulation quality in the foaming process. More field experiments prove that the ratio should be controlled between 1.15 and 1.18 to ensure the thermal insulation.