The wind turbine bearing runs under complicated loading and vibration condition and its design and analysis is a developing and crossing discipline. The typical main bearing arrangements for wind turbine are compared, including the 3-point arrangement with spherical roller bearing, double-row tapered roller bearing and cylindrical roller bearing, two single-row tapered roller bearings. The various factors including the wind turbine type, loading, cost and weight are considered in the design of wind turbine drive train. The influencing factor of bearing reliability and the relationship between wind load, drive train and bearing are studied. Based on an example of bearing reliability, the influence of complicated topography on wind load and bearing life is analyzed. The commonality of the wind farms with wind turbine failure is found, i.e. the topology and the wind condition of most wind turbine sites are very unfavorable, e.g. with sleep slope, not enough distance between adjacent wind turbines. Such factors can cause abnormal wind shear and turbulence, which can bring unexpected load onto the bearing. The key factors in the analysis procedure of topography and wind resource are discussed.