The invention relates to a fluorine-free fabric water repellent with a branched structure and a preparation method of the fluorine-free fabric water repellent, and belongs to the technical field of textile printing and dyeing chemical industry. The water repellent has good durability and water repellent effect and comprises the following preparation steps: firstly drying and dewatering a mixed solution of organic siloxane and small-molecular polyalcohol under vacuum, adding diisocyanate and a catalyst after the mixed solution is cooled, then raising the temperature and enabling reaction to obtain a reaction system A; after the reaction system A is cooled, adding a long chain alkane chain extender, then raising the temperature and enabling reaction to obtain a reaction system B; after the reaction system B is cooled, firstly adding a hydrophilic chain extender and acetone for reaction, then adding an end-capping agent and continuously enabling reaction to obtain a reaction system C; after the reaction system C is cooled, firstly adding a neutralizing agent for neutralization, then adding water for emulsification and removing the acetone to obtain the fluorine-free fabric water repellent with the branched structure.