Abstract: Computer simulation is put up to analyze the effect of randomly holding points on cotton length measurement.The simulation results show that it is difficult to measure cotton length distribution by means of fibrograph because the average error on every point of measurement should be no larger than 0.08%.The staple length,quartile length,short fiber content and mean length can be obtained under certain circumstances.Their reproducibility is quite good with the confidence of 95% when(50 000) pieces of fiber sampling are conducted.It also shows that the variances of quartile length and mean length are smaller in the same range of sampling,and the reproducibility of mean length is 0.83 mm even when only(2 000) pieces of fiber sampling are performed.