DMZ low density solid free drilling fluid is mainly comprised of water, high molecular polymer and natural high molecular compound. It's density ranges from 0.999 to 1.004 g/cm 3. It possesses good quality of anti caving, protecting wall and flocculating. The problems occuring in small diameter wire line coring drilling, such as slurry cake in inner face of drilling rod, low carrying capability, high water loss and so on, can be solved with it.