The invention discloses an undertint open width pad dyeing technology for dacron jacquard. The technology comprises the following steps of alkali washing, stoving, bottoming, stoving, shaping and fixing color, and tentering; wherein the alkali washing step comprises steps of adding 2-3g/l of sodium carbonate, adding 1-2g/l of detergent, and washing in a rinsing machine; after stoving, the step moves on to bottoming, the bottoming step comprises steps of adding disperse dyes, padding, dyeing and stoving in a padding machine, wherein the stoving temperature is 78-82 DEG C; shaping and color fixing are carried out on the cloth processed in the former step, the shaping temperature is 195-200 DEG C, the shaping time is 38-42 seconds, and the width of the fabric is taken as the finished product width; the cloth processed in the former step enters a stenter for tentering so as to obtain the finished product. The undertint open width pad dyeing technology has the characteristics of short steps, low energy consumption, light contamination, good consistency of colored light, and high efficiency; the step of shaping is for fixing color of the dye, so that steps of baking and washing are saved, the processes are shortened, and water consumption and energy consumption are lowered.