Abstract: The double row self-aligning roller bearing (DRSRB) is widely used in the field of low speed and heavy load rotating machinery. The structure of such bearing is very complex and researches on this kind of bearing are very few. Besides the fatigue lifetime calculating model for this bearing is lacking as well. In the real manufacturing process, the roller diameter of the bearing inevitably has a certain size of error, which has a great influence on the mechanical properties and fatigue lifetime of the bearing. In this paper, a calculating method for the mechanical properties and fatigue lifetime of the DRSRB has been established relying on the mechanical analysis and elastic deformation analysis with considering radial load, axial load, inner ring tilting and roller diameter error. The effects of roller diameter error on the fatigue lifetime of DRSRB are studied with a specific example. The results show that in the case of a positive diameter error, the maximum load of the off-sized roller and the load value in the whole load experience are higher than that without diameter errors. While a single roller with a negative diameter error shows an opposite results. The fatigue lifetime of the bearing becomes shorter when a single roller has positive or negative diameter error. When the diameters of the rollers have random distribution errors, the loads of all the rollers are not equal, and the difference in load between the rollers increases with the error band. While the fatigue lifetime of the bearing is reduced with the increase in the random distribution error band.