Drilling fluid recovery technology was applied in a horizontal well drilling process in Dongsheng gas field, by means of electrochemical treatment, precipitation and performance adjusting by reagent feeding; drilling fluid was recycled through harmless treatment to reduce wastes pollution. But the solid particles with diameters less than 5μm were still remained and drilling fluid would be polluted by these particles accumulation. The contaminated drilling fluid would lead to downhole accidents to increase drilling cost even well abandonment. Potassium chloride polymer drilling fluid system was applied for testing to solve borehole wall instability and lost circulation, which provides reference basis to reasonable application of drilling fluid recovery technology and potassium chloride polymer drilling fluid system.