A brand new performance assessment model is proposed for multiple sequence alignment. The new strategy is based on beam constructing of DC-BTA algorithm, which is a Divide-and-Conquer alignment method with beams. Beams form blocks of almost the identical columns and contribute biggest similarity weight to sequences. A formula to compute all beam areas covering a sequence assigns a value or weight to the sequence. And the total beam area is a partial to the whole alignment. A rate value between 0 and 1 is computed to assess the performance. This scheme is a simple and effective assessment policy in DC-BTA for the convenience of collecting the beam areas.