The invention provides a precast staircase formwork with the vertical step face height being adjustable. The precast staircase formwork comprises a contour formwork, a stair formwork and a supportingdevice. The stair formwork comprises a top step plate, a bottom step plate, middle step plates and adjusting plates; the top step plate is connected with the top of the contour formwork, the multiplemiddle step plates are arranged between the top step plate and the bottom step plate in a stair shape, and the bottom step plate is connected with the bottom of the contour formwork; opposite mountingnotches are formed between every two step plates, and each adjusting plate is arranged between the two corresponding opposite mounting notches; and the supporting device supports the contour formworkand the stair formworks. The precast staircase formwork has the advantages that the precast staircase formwork is simple in structure, small in weight, good in fixing effect and easy to mount, the using range of the formwork is expanded, and precasting of stair flights under the situation of various vertical step face heights can be met; and rigidity is high, connection is firm, the precast forming effect is good, the number of turnover times is large, and the working efficiency can be improved.