Terahertz communication can provide high speed, low latency, and high-capacity data transmission. The terahertz band is a potential band for the sixth-generation communication system (6G), so it is important to measure and analyze the terahertz channel. In this paper, the channel reflection loss of three materials, brushed stainless steel, non-brushed stainless steel, and white paper, is tested in an indoor environment using a 230–330 GHz communication system when the dimensions of incidence angle and distance are varied simultaneously. The test results are compared and analyzed with the path loss model in a line-of-sight (LOS) environment and free space path loss (FSPL) respectively. The results show that during the reflection channel measurement when the incident angle varies in a small angle range (0°–30°), the main factor causing the channel loss is still the path distance. In addition, the fit between the observed data and the floating-intercept (FI) theoretical model is analyzed, and it can be seen that the channel loss caused by the roughness of the reflector surface is larger than that caused by the small variation of the incident angle. Finally, an observation of the reflection characteristics of terahertz channels is made.