Based on methods of spatial autocorrelation, semi-variance function and the fractal dimension as well as the data of soil available phosphorus in 2000 and 2014, the spatiotemporal variation and environmental risks of soil available phosphorus in Karst tobacco-planting region in Xiangxi of Hunan were studied. The results showed that, during the 14 years, soil available phosphorus content increased by 30.89 mg/kg; the Z scores of soil available phosphorus index decreased, fractal dimension and the nugget effect increased, indicating a weaker spatial structure and stronger stochastic variability; the areas of ‘extremely high’, ‘very high’ and ‘high’ levels were increased by 28.36%, 26.89% and 25.94%, while the areas of ‘low’ and ‘very low’ levels decreased by 57.45% and 27.12%, respectively; There were significant correlation between soil available phosphorus and elevation, soil parent material, land use type, rotation mode and SOM content; Probability of soil available phosphorus content exceed the risk critical value increased greatly, the total areas of very high risk (probability >80%), high risk (probability 60% - 80%) and medium risk (probability 40% - 60%) accounted for 1.77%, 5.40% and 13.96% of the total study area, respectively. North of Longshan and east of Yongshun are the key regions to control agricultural non-point pollution of phosphorus.