A cooling system for computer, a cooling apparatus and a cooling method are described. The cooling system includes a computer casing, a fan and the fan-less cooling apparatus. The fan-less cooling apparatus has an air passage with two open ends and a closed circumference. The air passage passes a heat dissipating part of the apparatus, one end of the air passage communicates with air outside the computer casing and the other end communicates with air inside the computer casing. a plurality of blowholes for the fan and the air passage are formed in the computer casing. There is at least one fan. Air is blown inside or outside through the blowholes, which causes a pressure difference between the interior and the exterior of the computer casing. The pressure difference leads an air flow to flow through the blowholes to dissipate heat.