Mini-LED　backlights　energized　by　quantum-dot　color　conversion　(QDCC)　hold　great　potential　for　technological　breakthroughs　of　liquid　crystal　displays.　However,　luminance　uniformity　issues　should　still　be　urgently　solved　owing　to　the　large　interval　of　direct-lit　mini-LEDs,　especially　when　covering　with　a　QDCC　film　(QDCCF)　with　uniform　thickness.　Herein,　we　propose　a　uniformity　improvement　approach　of　mini-LED　backlights　by　employing　a　QDCCF　with　nonuniform　thickness　based　on　the　Lambertian　distribution　of　mini-LEDs,　which　is　demonstrated　by　screen-printing　preparation　and　ray-tracing　simulation.　Experimental　results　show　that　the　luminance　uniformity　of　the　nonuniform　QDCCF　can　reach　89.91%,　which　is　24.92%　higher　than　the　uniform　one.　Ray-tracing　simulation　further　elaborates　the　mechanism　of　this　significant　improvement.　Finally,　by　employing　this　nonuniform　QDCCF,　a　mini-LED　backlight　prototype　is　assembled　and　achieves　high　uniformity　of　92.15%,　good　white　balance　with　color　coordinates　of　(0.3482,　0.3137),　and　high　color　gamut　of　109%　NTSC.　This　work　should　shed　some　new　light　on　mini-LED-based　display　technology.　©　2023　Optica　Publishing　Group.