AMC (adaptive modulation and coding) is a well-known technique that selects a suitable modulation level and coding rate according to the userpsilas channel quality. The utilization of AMC in DL (downlink) requires the DL channel information of each user to properly select the MCS (modulation and coding scheme) level. However, under a practical OFDMA system environment, it is unsuitable to feed back all the channel information over the whole frequency resources due to the limited uplink bandwidth. In this paper, to optimize the performance of the AMC system we propose a FBL (flexible block-wise loading) algorithm combined with a novel CQI (channel quality information) feedback scheme with a reduced number of required bit. The proposed FBL algorithm dynamically allocates groups of sub-carriers to each user based on the channel quality information in a newly defined feedback signal format, thereby improving the sector throughput and outage probability performance.