The invention belongs to the field of chemistry and discloses a special binder for an aramid fiber braided layer and a preparation method thereof. The semi-finished binder is prepared from 30 to 50 weight parts of polyurethane solid gum, 50 to 60 weight parts of acrylic ester and 50 to 100 weight parts of ethyl acetate and by adding isocyanate in an amount which is 1 to 10 percent based on the total weight of the semi-finished product. The preparation method comprises the following steps of: pumping the 30 to 50 weight parts of polyurethane solid gum, 50 to 60 weight parts of acrylic ester and 50 to 100 weight parts of ethyl acetate which are accurately weighed into a reactor by using a pump, heating the mixed materials for 60 to 80min with stirring, continuously stirring for 5 to 15min, and cooling to obtain the semi-finished product of the binder; and in use, adding the isocyanate in an amount which is 1 to 10 percent based on the total weight of the semi-finished product into the semi-finished product, and obtaining the finished product of the binder by uniformly stirring. The binder of the invention is designed for aramid fibers, uses widely available materials, is simply prepared, can be applied to rubber industry and also can be applied to many fields such as communication optical cable and handicrafts manufacturing.