A flat light module and the manufacturing method thereof are disclosed. A first substrate and a second substrate with a plurality of electrodes are assembled. The discharge gas is filled between both substrates. A first dielectric layer with a first pattern and a second dielectric layer with a second pattern are covered on the electrodes in order, wherein the first pattern is used as a stopper and the second pattern is used as a mask to remove a portion of the second dielectric layer to form a plurality of protrusions and to expose a portion of surface of the second dielectric layer. Next, the first pattern and the second pattern are removed to expose a portion of surface of the first dielectric layer and the second dielectric layer, and then a fluorescent layer is coated on the exposed surfaces, the upper surface of the second substrate except for the surface of forming the electrodes and the first dielectric layer. The manufacturing method of the flat light module can simplify the manufacturing process and reduce the manufacturing time and cost.