In this study, a model for a heavy industrial factory in an International Telecommunication Union-Radiocommunication (ITU-R) building entry loss (BEL) model is developed. In addition, a new parameter of a reflected power (RP) is proposed and modeled for prediction of an outdoor-to-indoor (O2I) path loss on non-line-of-sight (nLoS) environments. To examine the BEL model on a factory environment, BEL measurements were carried out at frequency range of 3 to 24 GHz. The BEL characteristics are analyzed and the parameters of the model are extracted from the measurement results. As the result of analysis, it reveals that the BEL model for the heavy industrial factory is significantly different from that of the traditional building in the ITU-R BEL model. A new classification of the building may be required for the industrial applications. Additionally, in order to investigate the impacts of the external environment on the BEL and whole propagation loss, a measurement campaign is proposed according to the presence and absence of the main clutter (a big training ship) behind the targeted building. The BEL measurements were performed and analyzed on the nLoS path and being compared with the line-of-sight (LoS) path from 3 to 24 GHz. The proposed parameter, RP, is developed and extracted by using the measurement results. The results confirmed that the error is significantly decreased when the RP parameter is added rather predicting the excess loss (EL) only by the sum of BEL and clutter loss (CL). The prediction model is proposed for the O2I path loss on the nLoS environment.