Studies have shown that solar thermal power generation (STPG) can partially replace conventional power generation techniques, thus solving the global problem of energy shortage. Targeting a 70kW butterfly type STPG system, this paper discusses the impacts of solar radiation intensity on the concentrator, and analyses the economic efficiency of the system against such economic indices as internal rate of return (IRR), net present value (NPV) and levelized energy cost (LEC). The research results show that: When the solar radiation intensity is greater than 400W/m2, the proposed system can operate at above 70% of the full load without using natural gas; when the solar radiation intensity is greater than or equal to 700W/?, the system can operate at full load. The butterfly type STPG system requires more basic investment and has a longer payback period than common power generation systems. Besides, the combined generation mode incurs a far smaller energy cost (0.75kWh) than the generation mode dominated by solar power (2.045kWh). The on-grid electricity price has the greatest impact on the IRR and NPV, followed by basic system investment and natural gas price. The research findings lay the theoretical bases and provide economic references for the development of STPG systems.