The selection of an optimal combination of geophysical methods plays a very important role in the groundwater resources investigation and assessment. It provides information to determine the drilling locations, to evaluate groundwater resources as well as to define the distribution of aquifers, aquitard and the situation of the saline contaminated aquifers. In this paper the author presents some combination of the geophysical methods, which have been effectively used in investigation and evaluation of groundwater resources throughout the Vietnam by the National Center for water resources Planning and Investigation during the recent years. According to that, the author also introduces some principles for selecting optimal combinations of geophysical methods for some specific objects, which have been successfully used in groundwater resources investigation.