Abstract: The analysis of soil elements is of great significance in geological surveys, resource exploration and other fields. However, the simultaneous digestion and analysis of multiple elements including metals and rare earth elements (REEs) in a single process, often face challenges such as incomplete digestion of insoluble elements (e.g., REEs, Ba, Th) and interference from complex matrices in mass spectrometry. Although the traditional pressurized acid digestion method shows good recovery for elements like Li, Be, and Ti, the recovery rates of insoluble elements such as REEs are low (most <90%), making it difficult to meet the requirements for simultaneous analysis of general elements, heavy metal elements such as Pb, Cu, Zn and insoluble elements. In this work, by comparing the digestion effects of 15 acid digestion systems—composed of 4 mL of inverse aqua regia, different amounts of hydrofluoric acid and perchloric acid—and two kinds of acid removal conditions on 37 elements in national soil standard materials, an ultrawave digestion–four-acid system combined with ICP-MS/MS was established. The optimal conditions were determined as follows: 3 mL nitric acid + 1 mL hydrochloric acid + 2 mL hydrofluoric acid + 0.8 mL perchloric acid digestion system and multiple additions of nitric acid to strengthen the acid removal combination. This method effectively destroys silicate mineral structures, promotes the dissolution of refractory oxides, and removes residual hydrofluoric acid through repeated acid addition and high-temperature acid driving, thereby avoiding the formation of insoluble fluoride precipitates. The method was systematically validated using 8 national soil standard materials (including GBW07565) and rhizosphere soil from typical crops (Xizang highland barley, Xinjiang tomato, and Jiangxi rice). The results showed that this method can accurately determine 35 target elements, except for Cd and Cr, with a method detection limit of 0.0005–3.410 mg/kg and a relative standard deviation (RSD) of 0.25%–14.1%. The recovery for actual samples was 81.6%–107.4%, with an RSD of 0.2%–9.6%. These results indicate that the method has good stability and applicability. Compared with the traditional pressurized closed-acid digestion method, this method significantly improved the recovery rates of REEs, Ba, Th, and other elements (mostly > 90%), providing an efficient and reliable solution for multi-element analysis of soils with different matrices.