Firstly,the characteristics of the fault current of wind farms and its influencing factors are researched.Then considering the transition resistance ,the relational expression between fault current at the upstream side of wind farm network-connected position and short-circuit current offered by the wind farm is derived. Impacts of the shunting effect of wind farm on system fault current is analyzed. A simulation model of distribution network containing wind farm is built on the platform of PSCAD/EMTDC, and influence of wind farm on fault current and protective relaying at the upstream side of wind farm network-connected position are studied are simulated and studied.Research results show that on account of the shunting effect of wind farm, the fault current at the upstream side will decrease.when the situation is serious,it is connected to the system and protective relaying will refuse action because of the shortened I-zone and the Insensitive II-zone at the upstream side of wind farm network-connected position.