To reduce noise and make the structure of the car more rational, we established modal test system of car's body-in-white in this paper. Car body-in-white was mounted on rigid platform with four coil springs. The car was excited by an electromagnetic exciter. The method of single-point excitation and multi-point collecting vibration was used in this test. Excitation point was chosen in the bearing beam. Signals picked up by the acceleration sensors were processed in the software of Mescope. With this system, different modal frequencies and modal characteristics of the car are acquired. The results show that modal parameters are effective and reliable and those parameters can be basis for the designer to improve the structure of the car.