The invention relates to a method for dyeing a yarn containing cellulose fiber by reactive dye. In the method, the following processes are carried out on the yarn which is warped into a beam by a continuous pad dyeing mode: padding with cationic modified solution, drying, padding with staining solution, drying, baking, washing and drying, wherein, a drying cylinder is adopted in the baking process for baking in a contact manner, and the yarn is directly contacted with a high-temperature outer wall of the drying cylinder. By means of the method, continuous pad dyeing of the yarn containing cellulose fiber can be carried out by the reactive dye; the dyeing process has the advantages of relatively low baking temperature, simple baking mode and less broken yarns which are easily handled by an operator; and the adopted dye has the advantages of being free from restriction of K-type reactive dye, comprehensive color spectrum, wide selection range, simple auxiliaries without salt, urea and the like, less dye hydrolysis consumption, low wastewater chromaticity and stable dyeing quality, and deep, medium and light color can be dyed.