Abstract: In order to efficiently develop thin-bed heavy oil reservoirs which are characterized by high viscosity and large distribution range, the extension law of steam chamber after the adding of solvent and its effects on the production performance were investigated by means of 2D physical simulation technology based on the field parameters of one certain oilfield the moment the light solvent assisted steam flooding by horizontal well was soon conducted on site in the thin-bed heavy oil reservoir of the oilfield. And n-hexane (C6) solvent was taken as the light solvent. Then, in order to study the migration law of the solvent in the steam chamber and its effects on field temperature, viscosity field and oil saturation field, the solvent assisted steam flooding was numerically simulated by using the CMG-STARS module of CMG Company based on the parameters of 2D physical model. It is indicated that adding mono-component light solvent in the process of horizontal-well steam flooding in thin-bed heavy oil reservoirs can reduce the viscosity of crude oil inside and in front of the steam chamber effectively, so as to improve the steam absorption capacity and oil displacement efficiency along the direction of production well. Compared with the conventional steam flooding, the solvent assisted steam flooding by horizontal well is more advantageous with large volume of steam chamber, fast extension along the direction of steam injector, uniform extension along the direction of production well, fast breakthrough of steam front and large ultimate sweep area. In the process of production, there is nearly no stable production period and the oil production rate reaches the peak value when the steam front arrives at the production well, and then steam channeling occurs and oil production rate is lower in the stage of high water cut. The ultimate displacement efficiency is high. In conclusion, the solvent assisted steam flooding is superior to the conventional steam flooding, and it can reduce the in-place oil viscosity effectively and increase the sweep area of steam in reservoirs, so as to develop thin-bed heavy oil reservoirs more efficiently.