The foam system of an EPB shield machine manufactured by Mitsubishi Heavy Industries has some disadvantages, therefore reforms are made by referring to the design of the foam systems of shield machines manufactured by Herrenknecht A.G. In this way, the disadvantages of the original foam system are eliminated with the lowest cost. In the paper, the selection of the components of thefoam system based on calculation of the required capacities is presented. The principles and advantages/disadvantages of the original foam system and the reformed foam system, as well as the countermeasures for the malfunctions that may occur to thereformed foam system, are also presented.