In order to solve the problem that static attribute reduction cannot update attribute reduction efficiently when the number of attributes in the set-valued decision information system changes continuously， an incremental attribute reduction method with knowledge granularity as heuristic information was proposed. Firstly， the related concepts of the set-valued decision information system were introduced， then the definition of knowledge granularity was introduced， and its matrix representation method was extended to this system. Secondly， the update mechanism of incremental reduction was analyzed， and an incremental attribute reduction method was designed on the basis of knowledge granularity. Finally， three different datasets were selected for the experiments. When the number of attributes of the three datasets increased from 20% to 100%， the reduction time of the traditional non-incremental method was 54.84 s， 108.01 s， and 565.93 s respectively， and the reduction time of the incremental method was 7.57 s， 4.85 s， and 50.39 s respectively. Experimental results demonstrate that the proposed incremental method is more faster than the non-incremental method under the condition that the accuracy of attribute reduction is not affected.