Abstract: Because of the long drilling period and producing section, drilling fluid contamination in horizontal well is serious. The production effects of some sections have not lived up to expectations after well completion in horizontal wells, and general aciding treatment just could remove the inorganic blockages in drilling fluid. The degradation effects of enzyme on the polymers in drilling fluid such as starch, carboxymethyl cellulose, polyacrylamide and xanthan gum and that on the drilling cake were studied in lab experiments. Filed operation process and effect of removing drilling fluid contamination by enzyme immersion in horizontal well were detailed in this paper. The results show that the technique is feasible in cleaning the pollution and should expand the experiment scale, which has a bright application value in the future.