Abstract: This paper uses a total sample composed of 3 589 gamma-ray bursts to study the correlation between their duration and the hardness ratio. First, according to whether the duration (T₉₀) is greater than 2 s, we divide the total sample into two sub-samples as the long bursts and the short bursts. We study the correlation between hardness ratio and T₉₀ of the total sample, the long burst and the short burst sub-samples, respectively. The results are: for long-burst and short-burst sub-samples, there is no correlation between the hardness ratio and the T₉₀; therefore, the correlation between the hardness ratio and the T₉₀ of the total sample is caused by the differences between the two sub-samples. The results of this paper reveal the rationality of classifying GRBs into two types: long bursts and short bursts, and also imply the differences in the properties of long bursts and short bursts, supporting the view that long bursts and short bursts have different origins.