  In the present paper, we investigated the distribution of hardness ratio (HR)
for short and long gamma-ray bursts (GRBs) in different time scales for the
first two seconds. After including and subtracting the background count, we
performed a Kolmogorov--Smirnov (K-S) test to the HR distributions of the two
classes of GRBs in each time interval. Our analysis shows that the
probabilities of the KS test to the distributions are very small, suggesting
that the two classes of bursts are unlikely to arise from the same HR
distributions, and indicating that they probably originate from the different
physical processes and central engine. In addition, we found that the hardness
ratio of short bursts within the time interval of 0$-$0.96 seconds changes
hard-to-soft, on the other hand long bursts do not. The two kinds of bursts
have different characteristics in the first 2 seconds which might be associated
with different physical mechanisms.
