We reported the optical observations of GRB 121011A by 0.8-m TNT telescope at Xinglong observatory , China .
The light curve of optical afterglow shows a smooth and featureless bump during the epoch of \sim 130 sec and \sim 5000 sec with a rising index of 1.57 \pm 0.28 before the break time of 539 \pm 44 sec , and a decaying index of about 1.29 \pm 0.07 up to the end of our observations .
Meanwhile , the X-ray light curve decays in a single power-law with a slop of about 1.51 \pm 0.03 observed by XRT onboard Swift from 100 sec to about 10000 sec after the burst trigger .
The featureless optical light curve could be understood as an onset process under the external-shock model .
The typical frequency has been below or near the optical one before the deceleration time , and the cooling frequency is located between the optical and X-ray wavelengths .
The external medium density has a transition from a mixed stage of ISM and wind-type medium before the peak time to the ISM at the later phase .
The joint-analysis of X-ray and optical light curves shows that the emission from both frequencies are consistent with the prediction of the standard afterglow model without any energy injections , indicating that the central engine has stopped its activity and does not restart anymore after the prompt phase .