In this paper reference evaporation Penman-Monteith (FAO56) and meteorological parameters such as wind speed, sunshine duration, humidity, maximum and minimum temperature trends at monthly, seasonal and annual time scales were analyzed by using Spearman’s nonparametric test for four synoptic sites of Kurdistan province in Iran. For each time series, trend lines were extracted using Sen’s estimator. Also the sensitivity analysis of meteorological parameters was performed by step by step multiple linear regression method. Results indicated a significant increasing trend for reference evaporation in Sanandaj station.the slope of trend lines for Sanandaj, Zarinhe and Bijar stations were positive on the monthly, seasonal and annual time scales. In these three stations a significant increasing trend was also observed for both winter and summer seasons. Trend analysis of the maximum temperature of Bijar and Sanandaj stations revealed an increasing trend for warm season. Sunshine duration and maximum temperature were found to the most dominant variables influencing reference evaporation in Kordestan province.