In　recent　years,　Mini-LED　has　been　widely　used　in　direct-lit　backlight　for　Liquid　Crystal　Display　(LCD)　widely　due　to　its　advantages　of　miniaturization　and　low　power　consumption.　Typical　Mini-LED　direct-lit　backlights　mainly　rely　on　the　diffuser　plate　to　convert　point-like　light　sources　into　uniform　surface　light　sources.　However,　the　diffuser　plate　cannot　achieve　high　uniformity　at　a　very　low　optical　distance　(OD).　In　this　paper,　we　introduced　the　pyramidal　microstructure　and　the　semi-cylindrical　microstructure　to　both　sides　of　the　optical　film,　respectively.　The　mechanism　of　influence　of　the　pyramidal　microstructure　and　the　semi-cylindrical　microstructure　on　light　was　analyzed.　We　clarified　the　relationship　between　the　parameters　of　the　microstructure　(the　pyramid　angle,　the　pyramid　dimension)　and　the　illuminance　uniformity　by　simulation.　Moreover,　two　layers　of　microstructure　optical　films　are　discussed　and　simulated.　Through　the　simulation,　the　optical　effects　are　evaluated　and　analyzed　from　the　point　of　illuminance　uniformity.　Simulation　results　maintain　that　when　the　OD　is　5mm,　the　illuminance　uniformity　reaches　93.07%.　Compared　with　the　diffuser　plate　with　a　thickness　of　1.5T,　the　thickness　is　reduced　by　0.9mm,　and　the　illuminance　uniformity　is　increased　by　11.77%.　This　work　fully　demonstrates　the　advantages　of　the　microstructure　optical　film　to　improve　the　illuminance　uniformity.