Due to the prevalence of infectious diseases caused by viruses and bacteria, UV sterilization has been attracting attention. Since UV is invisible, the repeated prototyping, measurement, and sterilization testing involved in the product development is both time-consuming and costly. This paper discusses the effect of the light receiving surface spacing on the results of the analysis of UV integrated light exposure, and shows that the error increases as the light receiving surface spacing increases. We calculated the UV integrated light exposure of the water sterilizer, and found that, based on a 5 mm light receiving surface spacing, the error was 0.17% when the light receiving surface spacing was 100 mm and the reflectance of the component was 90%, and the error was 6.03% when the reflectance of the component was 30%. Next, using the average of the irradiance at three locations on the light receiving surface to calculate the UV integrated light exposure, we found that the maximum error was 0.51% when the reflectance of the component was 90%, and the maximum error was 23.89% when the reflectance of the component was 30%.We therefore recommend examining the analysis results by setting multiple patterns of light receiving surface spacing for the analytical model and performing optical simulations with light receiving surface spacing where the errors in the analytical values and the computational resources are acceptable. In addition, we describe the process of applying this analysis method to the development of UV sterilization equipment.