In this research, probabilistic fatigue load estimation by the aeroelastic modeling was carried out for a small wind turbine with 1m diameter. The results were compared with the simplified load model which is a deterministic method, and quantitative evaluation of the difference between two methods was presented. An aeroelastic simulation code for 5 bladed wind turbines is used for aeroelastic modeling. This code is based on NRELs FAST and modified for 5 bladed turbines by authors. On the fatigue analysis, wind condition is set to be IEC 61400-2 Ed.2 DLC1.1 which is assumed to be equivalent condition of simplified load model. From the time series results from aeroelastic analysis, the load amplitude and cycles are counted. Then the cycles are weighted by wind speed probability distribution correspond to IEC 61400-2 Class I to IV. The result from aeroelastic modelling was similar to one from simplified load model in Class I but different in other Classes. The reason is that the fatigue load in high wind speed, which is not encompassed with simplified load model, is dominant for fatigue load with target turbines model regardless of IEC Class. Therefore it is important to consider probability of wind speed over all operating condition in fatigue load estimation.