Millimeter wave transmission in particulate environment is a fundamental topic in the communication community. In order to make controllable measurement, a dual-reflector Gaussian beam transmission system is designed based on the quasi-optical theory. This system consists of a pair of multi-flare angle horns, and two ellipsoidal focusing reflectors. The multi-flare angle horns are employed to generate Gaussian beam with 96% Gaussianity, and the focusing reflectors transform the incident beam to be identical to the input beam. In addition, the measurement on the system loss is conducted in the range of 75~110 GHz by using a vector network analyzer and extenders. It is found that the system loss is in the range of 2~4 dB, showing a satisfactory transmission performance. The preliminary study on water-spraying paves the way for future controllable measurement.