Two-dimensional molybdenum disulfide (MoS2) is a promising material for ultrasensitive photodetector owing to its tunable band gap and high absorption coefficient. However, controlled synthesis of high quality, large area monolayer molybdenum disulfide (MoS2) is still a challenge in practical application. In this work, we report a gold foil assistant chemical vapor deposition (CVD) method of large size (>400 μm) single crystal MoS2 film on silicon dioxide (SiO2) substrate. The influence of Au foil in enlarging the size of single crystal MoS2 were investigated systemically using thermal simulation in Ansys workbench 16.0, including thermal conductivity, temperature difference and thermal relaxation time of the interface of SiO2 substrate and Au foil, which indicated that Au foil could increase the temperature of the SiO2 substrate rapidly and decrease the temperature difference between the oven and substrate. At last, the property of the monolayer MoS2 film was further confirmed by the back-gated field effect transistors (FETs), a high photo-response of 15.6 A/W and a fast photo-response time of 100 ms was obtained. The growth techniques described in this study could be benefit for the development of other atomically thin two-dimensional transition metal dichalcogenides (TMD) materials.