The utility model relates to a balance valve assembling device of a cold and hot water mixing valve, which is characterized in that a dent is arranged in the footwall of the box body of a mixing valve to contain a balance valve cover plate, wherein, a lower seat pit of a concave balance valve is arranged above the cold-hot water inlet of the dent, and an upper seat pit of the concave balance valve is arranged below the cold-hot water inlet of the balance valve cover plate. The two components are provided with a seal between the joint surfaces in combining, so the lower seat pit of the balance valve of the box body and the upper seat pit of the balance valve of the plate form leak-stopping space together, while a balance valve body can be fixed in the leak-stopping space to achieve the goals that the assembling is simple and quick and the conformation is confirmed, steady and unease loosened after assembling.