Applications based on the formation of exciton polariton in microcavities provide new avenues for the realization of low-energy consumption and ultrafast devices in areas of photo-electronic and quantum information. Here, we propose a way to design polaritonic multi-mode interferometers in a WS2 microcavity by an all optical control method. The interference phenomenon of polariton is controlled by the well-known optical Stark effect. The optical Stark light changes dispersion (e.g., effective refractive index) of the illuminated region, and generates a waveguide region therein, thus supporting different guided modes of polariton. Multi-mode interference of polariton is then guided by changing the beam pattern or intensity of the Stark light. This proposed method is then theoretically analyzed and proved via effective refractive index calculation and eigenmode analysis of plane waveguide.