Lightweight foam concrete has been widely applied in the field of geotechnical engineering in the last decade or so, but relatively little research has been carried out on the selection and optimal proportioning of foam agent solutions. In this paper, the surface tension, foaming multiplicity, half-life and stability of the foam produced by several typical foam agents are studied systematically, and the performance indicators and concentration values of the preferred foam agents are proposed. In this paper, the surface tension, foaming rate, half-life and foam stability of several typical foam agents were systematically studied, and the optimum performance index and concentration value of foam agents were proposed. On this basis, with the C40 soil-cement mix ratio as reference, the prepared foam and C40 cement grout were mixed according to different injection volume ratios, and the dry and wet weights were measured to determine the ratio scheme of lightweight foamed concrete under different design weights. Furthermore, unconfined compressive strength tests were carried out to determine the compressive strength values of lightweight foamed concrete specimens under different stress conditions, and scanning electron microscopy tests were conducted to understand the microstructure of the specimens. The results show that the optimal concentration of foam agent is about 3%, foaming rate is 25, surface tension is 32mN/m, half-life is 15min. The density and strength of lightweight foamed concrete decreased significantly with the increase of foam injection rate, and the dispersion of bubble population and pore size increased significantly. The dry density of lightweight foamed concrete has a decaying exponential relationship with the injection rate, and the unconfined uniaxial compressive strength has a non-gentle and progressive exponential relationship with the dry density of lightweight foamed concrete. The empirical formulas can be fitted by nonlinear curves to be applied in geotechnical engineering. On this basis, the prepared foam is mixed with C40 cement slurry at different injection volume ratios, and its dry and wet weights are measured to determine the proportioning scheme for lightweight foam concrete under different design weight conditions. Further, unconfined compressive strength tests are carried out to determine the compressive strength of the lightweight foam concrete at different weights. Electronic microscope scanning tests are carried out to investigate the microstructure. The test results show that the optimum concentration of foam agent is approximately 3%, the foaming multiplicity is 25, the surface tension is 32 mN/m and the half-life is 15 min. The density and strength of lightweight foam concrete decrease significantly with increasing of foam injection rate, and the corresponding bubble group content and pore size dispersion increased significantly. The dry density of lightweight foamed concrete has a decaying exponential relationship with the injection rate, and the unconfined uniaxial compressive strength has a non-gentle and progressive exponential relationship with the dry density of lightweight foamed concrete.