Groundbased GPS technology has recognized as a tool to observe the atmosphere water vapor with the highest potential. The zenith wet delay (ZWD) is the key factor to obtain water vapor with high precision. The BERNESE software developed by the Astronomical Institute, University of Bern is one of most distinguishing means for calculating ZWD. The basic steps and relevant settings using the BERNESE software to calculate ZWD are introduced on the basis of the data from the continuously operating reference stations over Hongkong, and some special cases are studied, such as having meteorological observation files and calculating ZWD continuously for adjacent days and weeks, or calculating ZWD at some specific time points. The results indicate that the BERNESE software can be used to calculate ZWD perfectly.