The invention discloses a direct backlight formed by the arrangement of LEDs with gradually changed distance, comprising a backlight cavity, the front surface of the backlight cavity is provided with an optical membrane group, the back surface of the backlight cavity is provided with an LED fixing board, an LED lamp is arranged on the LED fixing board, the distances between adjacent LED lamps areall gradually reduced along the left and right and the upward and downward directions of the central lines along the row and column directions of the LED fixing board. During design, the maximum distance between adjacent LED lamps along the row and column directions can be determined according to the requirements such as the illuminating characteristic of the LED, the effective height of the backlight cavity, the diffusion capability of a diffusion film/plate, and the uniformity of mixed light, while the gradual change mode of the distance can be designed or calculated and simulated by adopting a certain simple function or a plurality of simple functions, LED arrangement needs to consider the requirement of a driving circuit, and the LED backlight with excellent optical uniformity can be obtained by combining the design with the optical membrane group.