The invention discloses a heat dissipation method for a switching mode power supply, and the method comprises following contents: 1) the switching mode power supply works, a cooling fan starts to rotate, the temperature of a heating device in the switching mode power supply rises with the the work time of the switching mode power supply, when the temperature of the heating device in the switching mode power supply is over 40 DEG C, vinegar in an air bag in a sliding groove boils to generate gas so as to enable the air bag to inflate, the inflated air bag pushes a sliding block on a lower fan blade to slide on the sliding groove, an upper fan blade and the lower fan blade are staggered, and the quantity of wind is increased; 2) the temperature of the heating device is reduced, the gas generated by the vinegar in the air bag starts to reduce, the air bag starts to contract, the upper fan blade and the lower fan blade gradually overlap, and the quantity of the wind is reduced; 3) the switching mode power supply stops working, the cooling fan stops rotating, the gas in the air bag cools to form liquid, the air bag contracts, the sliding block resets, and the upper fan blade and the lower fan blade completely overlap. According to the invention, the scheme can solves a problem that a switching mode power supply module heat dissipation device can not regulate wind quantity according to the temperature rising variation.