Because of the thick soft silt layer in upper part of the borehole, a mud pool should be set up at the mouth in the construction of rotary bored grouting pile to keep the mud surface height in the borehole. The mud performance is the foundation to ensure the drilling quality, the performance indicators monitoring should be strengthened in the construction, and mud purifying device may be used if necessary. Reasonable selection of steel protective pipe embedding length and drilling parameters can not only ensure the construction quality, but also can greatly reduce the construction cost.