In bus protection improvement,Aiming at the problem of bus line in commissioned windfarm,by the improvement of the conventional bus protection algorithm and grounding mode of thesmall current grounding system,puts forward improvement schemes of medium and low voltage busbar protection based on distributed protection. The application result shows that the scheme not onlysolve the problem of insufficient sensitivity of single -phase grounding fault in small currentgrounding system,but also greatly reduces improvement cost and time.