Abstract: The completion of lateral drilling technology is hanging small casing with particular sizes in original production casing. The accidents treatment in these wells is very difficult since the well bore is featured by large size differences for inner diameter in upper and down section and small operated spaces for accident section. So this paper starts with the following aspects: tool design, operated string selection and circulatory cuttings carrying, and summarizes a set of process scheme which is suit for handling the complex accidents in sidetracking slim hole. The application have arrived prospective effect.