The invention discloses a method for improving the huff-and-puff recovery efficiency of shale oil by a carbon dioxide/cosolvent system. The method comprises the following steps that (1), the carbon dioxide/cosolvent system is prepared, specifically, a cosolvent with a set volume is added to a visual container, carbon dioxide with a set volume is introduced until the cosolvent is mixed with the carbon dioxide, and the pressure inside the visible container at the moment is recorded; (2), the carbon dioxide/cosolvent system is injected, specifically, the visible container is connected to an injection well to the set time to enable the carbon dioxide/cosolvent system to enter a shale oil reservoir, and pressure changes in the visible container are recorded by a pressure sensor; (3), a well isopened to produce, specifically, after the communication between the visual container and the injection well is balanced to the set time, a communication valve between the visual container and the injection well is closed, a valve of a production well is opened, the well is opened to produce, and the oil production is recorded; and (4), the steps 1 to 3 are repeated for multiple huff-and-puff operations to improve the recovery efficiency of the shale oil. According to the method for improving the huff-and-puff recovery efficiency of the shale oil by using the carbon dioxide/cosolvent system, the cosolvent is used for assisting the carbon dioxide for huff-and-puff, the soak time is reduced greatly, the huff-and-puff recovery efficiency is increased, and the number of times of the huff-and-puff is reduced, so that the production efficiency is improved.