Aimed to the complex strata of Pulang copper mining area of Shangri-La, and by the experimental date and theoretical analysis, the solid-free polymer drilling fluid consisting of host agent (vegetable-gum) and assistant agents(PAM & LP) was fixed, which was applied in the wire-line drilling construction for ZK0409, the drilling difficulties in complex strata of Pulang copper mining area of Shangri-La were vercome. The paper discussed the optimum formula of the solid-free polymer drilling fluid and analyzed its action mechanism in complex strata.