A computer module includes a housing having a cover defining a condenser chamber, and a heat-absorbing unit having at least one cavity body adapted to contact a heat source, and a working fluid received in the cavity body. A tubing unit is connected fluidly to the condenser chamber and the heat-absorbing unit. The working fluid flows through the tubing unit to circulate from the condenser chamber to the heat-absorbing unit by gravity and from the heat-absorbing unit to the condenser chamber by natural convection. The tubing unit forms a closed circulating loop with the heat-absorbing unit and the condenser chamber. The cover is adapted to exchange heat with external cold air so as to condense the working fluid in the condenser chamber.