In this paper, one of the most important climatic elements, water vapor pressure, has been analyzed. In this contest Mann-Kendall and Sen's Slope Estimator techniques are used to analyze the water vapor pressure trend and it's change's slope in the South and South West of Iran. Accordingly, 12 stations along the 44-year period (1967 to 2010) for stations analysis and 47 stations along the 16-year period for spatial survey were tested. To calculation Mann-Kendall and Sen's Slope Estimator tests on the whole study area, it was divided into the optimal spatial resolution, cells by 9 × 9 km resolution (3,338 cells), and then the monthly, seasonal and annual WVP time series were extracted by MATLAB software. After preparation of the matrix by size 30 × 3338, Mann-Kendall and Sen's slope estimator tests were done on all cells and after evaluating different geostatistical methods such as IDW, Kriging and RBF, the most efficient method, kriging, was chosen to derivation of maps.The results indicated that the upward trend of water vapor pressure was in the coastal areas of the Persian Gulf and especially the Boushehr province. On the other hand, the significant downward trend was observed based on the heights, especially the Zagros highlands.