Carboxymethyl cellulose sodium salt in the main for drilling fluid viscous drop filter lost agent, carboxymethyl cellulose sodium salt long chain with multiple clay particles can absorb, can increase mud cake of the cementing sex, can restrain shale hydration expansion and consolidate the role of the wall. Sodium carboxyl methyl cellulose salt solution has many excellent properties and chemical stability, not easy corrosion metamorphism, for physical security harmless, with floating and stable emulsification, good bonding and salt resistance ability, to the oil and organic solvent good stability.