It is a difficult technical problem for drilling in deep overburden layer with light rig and collecting core in the western mountains. Pore-formation became more difficult with collapsing and drill burying in deeper drilling. By the reasonable design and improvement on mud protection, the borehole reached the depth. The application results show that the drilling hole design was divided into 4-stages variable diameter, drilling with bits of different materials; SM-KHm ultra-low solid-phase slurry-supported was adopted in the alluvial medium-fine sand layer and diluvia gravel soil layer for borehole stability; the maximum drilling depth reached 22354m with more than 95% collecting rate of drill core.