The present disclosure discloses a method for changing a landscape signal of a liquid crystal screen to a portrait mode. The method comprises: adjusting the setting of a built-in driving TCON (time controller) IC (chipset) of the LCD so as to change the input signal interface of the LCD from an MIPI (mobile industry processor interface) to a TTL (transistor-transistor level) data/timing interface+SPI (serial peripheral interface) command control interface; controlling the initialization, turning-on and turning-off of the driving TCON IC via the SPI interface, and realizing the switching among four projection modes, desktop front projection, desktop rear projection, ceiling front projection, and ceiling rear projection, by adjusting the up, down, left and right display directions of a screen output image; receiving, in real time, the landscape image outputted by a front-end video processing chip through the TTL data interface, and then displaying same in real time.