The most used flocculants in treatment of waste drilling water are PAM flocculants. But its polymeric monomer often has toxicity. Gelatin is a non-toxic, amphipathic natural macromolecule. The flocculants prepared by gelatin and its application in waste drilling water has not been reported. In the experiment, gelatin was extracted from chrome shavings. Sulfate, citric acid and trypsinase were chosen to hydrolyze gelatin and then collagen solution was obtain. Then NaNO2 was added to seal amino of the collagen molecules. The flocculation effects of collagen solution before and after sealing amino on waste drilling fluid was estimated by its CODcr removal rate and the concentration of suspended solids. The results indicated that after sealing amino, the flocculation effect on waste drilling fluid decreased obviously. And when trypsinase was used as hydrolytic agent, the treatment effect on waste drilling fluid was better. The optimal hydrolysis condition was: pH was 7~7.5, temperature was 37°C, reaction time was 3h and the dosage of trypsinase was 1.5% of the gelatin. Under this condition, the CODcr removal rate was 46.7% and the suspended solid content of waste drilling fluid decreased from 2607mg/L to 730mg/L.