A formwork for pouring arched concrete precast beam slabs comprises an inner arched formwork body and an outer arched formwork body, truss type surrounding purlins are arranged on the inner side of the inner arched formwork body, a plurality of steel pipe surrounding purlins are arranged on the outer side of the outer arched formwork body, and a plurality of tension bars are connected and fixed with the truss type surrounding purlins and the steel pipe surrounding purlins after penetrating through the inner arched formwork body and the outer arched formwork body. The arc-shaped truss type surrounding purlins are installed on the back of the arc-shaped formwork to form the precast beam slab formwork which is stable in whole structure, therefore, the concrete quality defects of dislocation, curtaining and poor moulding appearance caused by displacement and deformation of the formwork in the process of pouring concrete are overcome, the appearance requirement for an arc-shaped structure is met, and the difficulty and the input for repairing the surface of the concrete at the later period are reduced.