The invention relates to a testing method for the fibrillation of fibers. A fiber bundle is treated by adopting an ultrasonic oscillation method; the fibrillation degree is tested and is an average value of fibrillation indexes F of the fibers in the fiber bundle; a point formed by fixing multiple fibers on the fiber bundle is used as a bundling point; minimum lengths of fiber segments between two ends of the fiber bundle and the bundling point are a and b, corresponding maximum lengths are c and d, the ratio of (c-a) to a is less than or equal to 10 percent and the ratio of (d-b) to b is less than or equal to 10 percent; the length of the fiber segment with the minimum length between the end of the fiber bundle and the bundling point is 0.45 to 0.55 that of the fiber. Testing results show that fibrillation conditions of all the fibers in randomly-selected 50 fibers are relatively uniform and are far higher than the level of the prior art. By using the testing method disclosed by the invention, the fibrillation degree of the fibers can be characterized more accurately; the testing method has the advantages of simplicity and convenience in operation, high efficiency and small testing errors.