Abstract: Millimeter-wave (mm Wave) band can offer ultra-high-speed wireless data transmission, which is considered as an important candidate band for the 5G mobile communication system. To gain further insights into mm Wave penetration characteristics, we present a series of penetration measurements at 28 GHz with 800 MHz bandwidth, a pair of 25 dBi horn antennas were placed on the two sides of the glass door. The penetration coefficients are measured for different incident angles and transmitter-receiver (Tx-Rx) spatial positions. This paper presents results stemming from a comparison between the measurement data and the Fresnel transmission formula coefficients which include ideal smooth surface model and proposed Gaussian rough surface model. The results illustrate that the Gaussian rough surface model proposed in this letter describes penetration performance of horizontal and vertical polarization signals more adequately. In addition, the effects of distances on the penetration coefficients are investigated, we also provide the penetration loss of different incident angles.