The present invention relates to a method in which the cave of a mountain is used as a chimney to pump updraft to generate electricity. The method utilizes a mountain body which is relatively more than hundreds of meters high, the mountain body is dug through from the top to the bottom, so that an interior chimney is formed, an air intake gate is arranged on the bottom of the chimney, therefore the tall mountain chimney can generate powerful pumping force to pump the relatively warm air on the ground into updraft which is exhausted through the top of the chimney, and in the process, the updraft can drive a turbine generator installed on the bottom of the chimney to generate electricity. As shown in the schematic diagram, the air in a glass house (figure 7) is heated by sunlight passing through glass, while the heated air is powerfully pumped by the mountain chimney (figure 4) into the updraft which flows through the gate (figure 1), a generator set (figure 2) and chimney channels (figure 3 and 4) to be exhausted out of the chimney, and in the process, the turbine generator is driven to operate and generate electricity. The method has the advantages of simplicity, convenience, low cost and no energy consumption, and the generated electric energy is clean energy.