Ground Based Augmentation System (GBAS) is a terminal area approach guidance facility designed to replace the traditional Instrument Landing System (ILS). One set of equipment can provide approach guidance service for multiple runways of the airport. For some large airports, two VDB transmitters are usually installed on the ground to increase system coverage. However, traditional flight inspection cannot identify which station emits the signal from the reception, which causes failure of station coverage evaluation. This paper proposes a multiple slot data analysis method based on EVSF1000 unit, which can analyze and evaluate the VDB signals of multiple ground stations in one flight by decoding and parsing data from 8 VDB time slots, to achieve the flight verification requirements of GBAS system with dual VDB stations. The method is verified in an GBAS inspection flight which completed the inspection of dual VDB stations installed in Tianjin Binhai Airport.