Precipitation could be regarded as a complex and a very vital element in the earth atmosphere and its spatial-temporal changes can control Iran''s climate. In the current research، in order to model the spatial-temporal changes of annual precipitation، the data taking from 50 synoptic stations، have been analyzed during the years 1966-2005، with a suitable distribution. The most data sequences are observed as climatic series having non-linear behavior which do not follow a normal distribution. Consequently، some non-parametric statistical methods were first applied to analyze of all data layers at hand. Then، for performance of the significance levels in annual precipitation trends، a non-parametric Mann-Kendal method was introduced. Subsequently، the area distribution of trend، moving mean average، humidity areas، and spatial precipitation changes of the lowest and highest areas mapped in an Arc GIS setting. Initial results show that the most synoptic stations trends are negatively increasing and some less reducing over Iran meaningfully. It was found that the maximum rate of reduction in trend values can be seen in the northern parts of the country، and inversely the maximum increasing trend rates are going to be established in the southern parts of the study area، during the last 40 years. Meanwhile، final findings well illustrate that the spatial changes in precipitation values، particularly in the arid and semi-arid areas، are significantly increasing. Regularly، since the year 1980، such changes have been accordingly intensified in the climatic sub-humid and very dry areas.