GRB021211 was first detected by HETE II and its early afterglow has been observed .
There is a break in its afterglow light curve at about 12 minutes after the bursts , before the break the optical flux decays with a power-law index of about - 1.6 , while at late time the power-law slope is about - 1 ( Chornock et al .
2002 ) .
Here we will show that the afterglow light curve of GRB021211 can be explained within the framework of the standard fireball model .
We show that the afterglow emission before the break time is the contribution of the emission from both the reverse shock and the forward shock , while the afterglow emission after the break time is mainly due to the forward shock emission .
From the fitting we can give constraints on the parameters : the initial Lorentz factor 250 \leq \gamma _ { 0 } \leq 900 , and the surrounding medium density n \geq 1.6 \times 10 ^ { -3 } atoms { cm ^ { -3 } } .
We propose that since the values of \epsilon _ { B } and \epsilon _ { e } are somewhat smaller for GRB021211 , so the peak energy of the reverse shock emission is well below the optical band , and thus it is substantially fainter than 990123 at similar epochs .
Also we suggest that such a break might be a common feature in early optical afterglows .