The main elements of the dismountable support system for working pit are introduced including 2 parts of vertical hollow column and special steel plate with uneven thickness. The vertical hollow column can be laid into the expected depth by force transfer device, air hammer or small drill. The special steel plate is laid layer by layer through stratified excavation. Structure type, working principle, construction technology and design theory are introduced and the design process is described combined with engineering example. The feasibility of column selection and rationality of the special steel plate size are verified according to the actual calculation to avoid the complexity of traditional construction technology, save engineering materials, improve construction efficiency and reduce project cost.