As the fact that the traditional two-layer prism films can not enhance the brightness of the MiniLED backlight obviously, a thin film with microstructure was designed to substitute for two-layer prism films.Firstly, based on the luminous distribution and the size of the MiniLED die, the microstructure was designed into two parts. For the region as wide as MiniLED die, the microstructure was designed as the prism with 90°vertex. For the region between the two MiniLed dies, the MiniLED die was taken as an extended source and the light emitted from the two endpoints of the MiniLED die reached a certain point of the microstructure and formed an angle. The light along the bisector was collimated to the axial direction. The microstructural profile was calculated combining the Snell’s law. After that, a single microstructure and array were modeled and simulated by LightTools. The simulated results show that the on-axis brightness increases by 31.3% compared with the two-layer prism films. Finally, the microstructure was fabricated by the maskless lithography device and tested by cofocal microscope. The experimental results show that the on-axis brightness increases by 25.7% compared with two-layer prism films. The thin film can help enhance brightness of MiniLED backlight module.