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Second harmonic generation (SHG) is an effective way to generate short wavelength laser with high power. SHG is accompanied by absorptions of fundamental waves and harmonic waves, which make a fraction of the two waves deposit energy as heat and cause a temperature gradient along the radial direction of the periodically poled potassium titanyl phosphate (PPKTP) crystal. The inhomogeneous temperature distribution causes thermal lensing in the crystal. The thermal lensing effect will deform the spatial mode of the SHG cavity and result in the mode-mismatching of the fundamental wave to the SHG cavity, and the conversion efficiency of SHG process is so reduced. Moreover, with the increase of injected fundamental wave power, the influence caused by thermal lens becomes more and more serious. In order to obtain a high-efficiency frequency conversion, it is necessary to take measures to minimize the effect caused by thermal lensing. In this paper, we report on a high efficiency generation of green laser at 532 nm by external cavity SHG process with a semi-monolithic standing cavity. The influence of thermal lens effect on the optimal conversion efficiency in different semi-monolithic cavities was theoretically analyzed. The variation of conversion efficiency with the pump power in "plane-concave" semi-monolithic cavity based on parallel crystal and "concave-concave" semi-monolithic cavity based on concave crystal was quantitatively analyzed. In experiments, two types of cavity structures were built to measure the variation of frequency doubling conversion efficiency with pump power. For the "plane-concave" semi-monolithic cavity, the maximum green laser power of 747 mW was obtained and the corresponding conversion efficiency reaches (93.43)%, with injecting of 800 mW infrared laser. For the "concave-concave" semi-monolithic cavity, the maximum green laser power of 529 mW was obtained and the corresponding conversion efficiency is (88.23)%, with injecting of 600 mW infrared laser. The results show that the thermal lens impacts on the optimal conversion efficiency more serious in "concave-concave" semi-monolithic cavity in comparing with "plane-concave" semi-monolithic cavity. What's more, the influence of thermal lens effect gets higher and higher with the increase of the loss in the cavity. It is obviously that the "plane-concave" semi-monolithic cavity is more suitable for the SHG process and has huge potential in quantum optics and cold atom physics and provides a guide for future research on high-efficiency SHG process.