Binary joint-transform correlator (JTC) is used to implement optical parallel Dempster's rule of combination computation. The corresponding theory and method about how to implement the orthogonal sum of the basic belief assignment has been discussed. The corresponding theory has been discussed, and computer-simulation results are presented, which prove this method is practical. Compared with the method John Caulfield proposed implementing an outer product by two crossed 1-D acoustooptic cells, this one benefits from the advantages of high accuracy because of the digital representation of the multiplied numbers and of the simplification in the optical process of Dempster's rule of combination computation because of the direct result of the orthogonal sum of basic belief assignment by the appropriate arrangement of the binary spaial code in the input plane of the joint transform correlator.