The invention relates to a double-vacuum unwatering precipitation system and method. The precipitation system comprises a pumping well, a plurality of radial vacuum preloading wells distributed in a precipitation area around the pumping well and a first sealing membrane covering the soil of the precipitation area; each radial vacuum preloading well comprises a preloading well casing, a plurality of circular holes distributed in the corresponding preloading well casing, second sealing membranes coating the side face and bottom of the corresponding preloading well casing and a filter material and filling fine stone which fill the portions outside the side face of the corresponding preloading well casing and under the corresponding preloading well casing respectively; the filter material in each radial vacuum preloading well is connected with a vacuum pump. Compared with the prior art, the double-vacuum unwatering precipitation system and method can accelerate the removal of water in thesoil when a vacuum unwatering well adopting well casing precipitation or separately adopting downhole vacuum pumping cannot meet the construction requirements in an underground water area to avoid thesituation of drying up during pumping, thereby making the underground water level lower than the construction requirements, making up for the deficiency of an existing method, and providing a new wayof the precipitation method for the fields of engineering geology, geotechnical engineering and foundation pit engineering.