Multi-layer Insulation (MLI) assemblies have excellent thermal insulation performance in high vacuum environment. Their excellent heat radiation and heat conduction insulation ability can provide an effective thermal protection for infrared opto-electronic equipment. So, they have extremely wide applications in aerospace. The insulation performance of a MLI assembly for space application with duplex aluminized polyester film is mainly tested in the high vacuum environment. The test has provided specific data for an engineering application.