Because the deficiency of the most mapping functions at low cutoff angles, it is necessary to develop new mapping functions so that the GPS observations at low cutoff angles could be used effectively. The dynamic mapping functions with spatial and temporal variety are also needed for the adaptability. Though we can get PWV (precipitable water vapor) with high accuracy, but it cannot provide three-dimensional distribution of water vapor in atmosphere. It has been proved that slant water vapor(SWV) contains vertical information of water vapor. The vertical distribution can be retrieved by tomography using SWV. In this paper, the techniques of how to determine SWV and analyze the threedimensional distribution using SWV and the main current problems are introduced. The assimilation of water vapor retrieved from GPS observations into numerical weather forecast is the main object of GPS meteorology and the forecast can be improved. The progresses of assimilation at present are also reviewed .The developments of monitoring global climate change and atmosphere refraction environment using GPS are also described.