The yarn tension is a key factor to accurately control carpet pile height, which changes with the yarn path and the path flexing. The purpose of this paper is to find the relationship between yarn path and yarn tension and provide a basis for the yarn tension controller design. Firstly, tufting equipment system components and basic principle of tufting carpet is introduced. Then, the yarn path during weaving tufting carpet including yarn feeding parts, yarn guiders and tufting needle is constructed and yarn flexing in the yarn path is analyzed. After discussing yarn tension change caused by the path flexing, it is concluded that yarn tension changes with the tufting needle position and periodic change with the yarn flexing periodic change.