The invention discloses a method for cutting a silicon rod through a diamond wire. During cutting, the diamond wire walks to completely cut the silicon rod in the positive direction and then walks in the reverse direction. During cutting, firstly, after the silicon rod to be cut is clamped tightly, the silicon rod slowly declines, when the lowest point of the silicon rod makes contact with a diamond wire net, the position is set as a cutter feeding zero point; secondly, the cutter feeding initial position is set as P, and P is larger than 0; and thirdly, when the silicon rod declines to the range of 0- -5 mm, the declining speed of a workbench is set as V1, the diamond wire walking speed is set as V2, the positive direction wire walking distance of the diamond wire is set as S, and the reverse walking distance of the diamond wire is set as S1. Due to the fact that during cutting, the diamond wire walks in the positive direction to completely cut the silicon rod and then walks in the reverse direction, left-right displacement caused by shaking during direction changing is avoided, and the problem that due to silicon rod size non-uniformity and zero point cutter adjusting reset deviation, the thickness of a silicon chip on the cutter feeding side is bad is solved.