The invention discloses a large-span fabricated mixed type steel open web sandwich plate floor system and a manufacturing method. The large-span fabricated mixed type steel open web sandwich plate floor system and the manufacturing method are low in cost. The floor system comprises a rectangular steel open web girder and a gridding frame mounted in the steel open web girder. The length Lx and the span Ly of the steel open web girder are larger than 1.5, a one-way stressed plate is constituted, and no common divisor exists between the length Lx and the span Ly of the steel open web girder. The gridding frame is composed of a plurality of units and comprises a square grid, a parallelogram grid and a quadrangle grid. A right angled isosceles triangle, an obtuse angle isosceles triangle and an acute angle isosceles triangle are included between the gridding frame and the steel open web girder. According to the large-span fabricated mixed type steel open web sandwich plate floor system and the manufacturing method, the effect that the large-span floor system has a mechanical model of a special plate can be ensured, and the purpose of steel saving is achieved.