Various studies suggest that the performances of TMDs are largely thickness dependent. In this paper, we develop a chemical vapor deposition method to synthesis monolayer and bilayer MoS2 flakes with a solution precursor. The MoS2 phototransistors were prepared to investigate their optoelectronic performance. The MoS2 photodetectors exhibit high detectivity of 2.44 x 10(11) and a fast response/recovery time of 97 ms/291 ms. The photoresponsivity of bilayer MoS2 flakes was found up to 7160 A W-1. Our research will pave a pathway to control the layer numbers of other TMDs nanostructures, expand the application of high performance 2D materials.