For the 3D printing requirements of complicated concrete structure components， the technology of combining washable formwork with existing conventional 3D printing concrete was proposed to realize spatial structure modeling， and the design process of washable formwork was optimized based on 3D printing cement based washable formwork performance tetrahedron model and analytic hierarchy process. By studying the influence of super absorbent polymer（SAP） and kaolin content in magnesium oxysulfide cement on the mechanical properties， printability， constructability and wash-ability of cement based materials， a 3D printing washable formwork of magnesium oxysulfide cement with good fluidity， printability and stable constructability was designed. Digital image correlation（DIC） method was used to dynamically monitor the time dependent deformation of washable formwork layer after printing. The time dependant deformation logarithmic model was established， which could provide technical reference for 3D printing concrete complex spatial construction.