Grain texture evolution during the directional solidification of Ni-base single crystal superalloy DD3 in spiral selector has been simulated by ProCAST&CAFE model. The results indicate that the main function of starter block is to optimize the grain orientations. The favorably <001> oriented grains would overgrow the unfavorable grains with increasing of the distance from the base of starter block, and when the distance is up to 26 mm, the average deviation of the grain orientations is controlled within 10?. Only one grain is allowed to grow into the cast by grain selecting in the spiral part, and no optimization occurs during grain orientation selection in the spiral. The grains near the outer wall of the spiral passage are always geometrically blocked by the spiral passage, and the grain near the inner wall of the spiral passage is usually selected as the final single crystal. It obviously depends on the location of the grains and has no apparent connection to the orientation of the grains whether the grains are selected or blocked in the spiral passage