A sound system for an up-and-down distributed sound-tight screen relates to a movie screen audio technology and consists of a sound box bracket, a middle sound box and a power amplifier. The objectiveof the invention is to solve the problem of mouth alignment of a sound-tight screen or an LED wall. The design utilizes the sound image positioning principle; according to the characteristic that thesound production point is basically located at the 2/3 height position of the screen when the picture person speaks, the middle sound box is divided into two groups or a plurality of groups of independent sound box units. The sound image points are positioned in the mouth shape distribution range by adjusting the parameters and the number of the two groups of centrally-arranged sound boxes, so that the mouth shape and the sound production points are ensured to be basically consistent when a picture person speaks, and the mouth shape problem can be solved without the need for a display systemto have a sound transmission function.