The invention discloses a processing method of soaking, vacuum pre-pressing and slurry injecting for sand piles of a collapsible loess foundation, which comprises the following steps: 1, manufacturing pile pipes in a collapsible loess stratum in a pre-pressing region, embedding a slurry injection steel pipe in each pile pipe, pouring sand at circumferences of the slurry injection steel pipes to form the sand piles, and laying a sand mat at the upper ends of all the sand piles while laying a vacuum extraction pipe; 2, digging sealing ditches at the periphery of the pre-pressing region, sequentially laying a first layer of geotextile, a diaphragm seal and a second layer of geotextile above the sand mat, backfilling clay layers and a heaping load body, filling water in the collapsible loess foundation of the sand piles, performing vacuum-pumping after saturation of the foundation, and completing consolidation and deformation under action of vacuum preloading; and 3, digging out the heaping load body, filling slurry into the slurry injection steel pipes, and pulling out the slurry injection steel pipes to form the slurry injected sand piles. The method provided by the invention has a better effect for the processing of the collapsible loess foundation.