A display method and a display device of dynamically controlling backlight are provided. The present disclosure obtains a modified grayscale value of the input image in each of partitions by using the whole backlight reference value, the RGBW grayscale values of the input image in each of partitions, the normalized backlight output brightness value, and the spatial distribution function of the backlight brightness in each of partitions. The normalized backlight output brightness value of each of partitions is processed as a real backlight output brightness value which is outputted to a backlight driving circuit. The modified grayscale value is processed as a real grayscale value and then the real grayscale value is outputted to a display panel for display. The backlight and image grayscale of each of partitions are adjusted dynamically, thereby improving contrast space and power consumption and further, normally displaying the HDR contents in the HDR display.