The characteristic of solar chimney power plant system is analyzed. For the key issue of low efficiency in solar chimney power plant system, a solar thermal power system with gas-liquid injector and hydroturbine is presented. This new system obtain the energy transferred process by gas-liquid injector. It is solar energy transformed into thermodynamic energy into potential energy and then into electricity. The density difference of work fluid is increased by gas-liquid phase transition in running process.The efficiency of solar thermal power generation is increased. In the case of the same cost, the theory power efficiency of new system increases one order of magnitude compared with the solar chimney power plant system. It proposes a new solution for large-scale application of solar thermal power technology.