Abstract: In order to study the application of the green environmental protection fluid solidified soil in engineering problems such as backfilling of a narrow fertilizer tank, the rice husk ash and geopolymer solidified engineering residue forming the fluid rice husk ash geopolymer solidified soil is proposed. The effects of the content and particle size of the rice husk ash on the unconfined compressive strength (UCS) of the rice husk ash geopolymer stabilized soil are examined by using the test methods of the unconfined compressive strength (UCS), X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray energy spectrum analysis (EDS), and the effects of the content and particle size of the rice husk ash on the microstructure of the soil are discussed. The results show that the net pulp fluidity of the rice husk ash geopolymer solidified soil is negatively correlated with the content and particle size of the rice husk ash, and the setting time is positively correlated with the content of the rice husk ash, but is negatively correlated with the particle size of the rice husk ash. The UCS value of the rice husk ash geopolymer stabilized soil increases significantly with the increase of the content of the rice husk ash and with the decrease of the particle size. When the content of the rice husk ash increases to 10%, the strength improvement efficiency decreases, and the optimal content of the rice husk ash is 10%. During the curing process, two kinds of gels, namely hydrated sodium aluminosilicate (N-A-S-H) and hydrated calcium silicate (C-S-H), play the role of filling the internal pores and cemented soil particles, so that the whole structure tends to be complete, which is the fundamental reason for the strength improvement of the rice husk ash geopolymer stabilized soil. The research results can provide a theoretical basis for the engineering application of the rice husk ash in fluid solidified soils.