The online sequencing problem of unbounded batch processing of incompatible workpieces with prospective intervals in a multi-unit flow shop is studied. Through the classification and discussion of combinatorial optimization method, the lower bound of the problem is obtained, and the competitive ratio analysis of the algorithm shows that it is the best possible online algorithm. For this problem, the lower bound 1+α is given, where α is the positive root of the equation (2f－1)α2+(f+β)α+β－f=0. Meanwhile, a best possible online algorithm Am(β) is provided. The feasibility of algorithm is illustrated by competitive ratio.