The complex water sensitive formation and broken rocks were encountered in the reconnaissance survey and detailed investigation areas of Shenxi manganese mine in Guizhou. On the premise of rational selection of drilling equipments, drilling parameters and proper operation, 2 solid-free flushing fluids of PHP-GSP and GPLS plant gums are used to have effectively prevented borehole diameter shrinkage and wall collapse, the friction resistance between drilling tools and borehole wall is reduced to avoid the downhole accident. Meanwhile the ROP is increased with the advantages of less flushing fluid material transfer, improved economic drilling efficiency and environmental protection. The paper introduces solid-free flushing fluids of PHP-GSP and GPLS plant gums about their action mechanism, compound methods and attentions in use.