The invention discloses a preparation method of a polyester fiber braided tube enhanced type composite hollow fiber forward osmotic membrane. The preparation method comprises the following steps of confecting a polymer, an organic additive, an inorganic additive and an organic solvent to be homogeneous membrane casting liquid according to a proportion; uniformly coating the membrane casting liquid on the outer wall and an internal pore canal of a polyester fiber braided tube, so as to obtain a braided tube of which the inner wall and the outer wall are coated with membranes; making the membrane coated braided tube pass a certain air residence time and then enter a coagulation bath to carry out phase-inversion membrane formation; soaking a primarily formed membrane in deionized water to remove the residual organic solvent, soaking the primarily formed membrane in a hot water bath, finally, soaking the primarily formed membrane in a glycerol aqueous solution, and then taking out and airing the primarily formed membrane, so that the polyester fiber braided tube enhanced type composite hollow fiber forward osmotic membrane is made. According to the preparation method, polymer membrane casting liquid is coated on the inner wall and the outer wall of the braided tube in a one-step manner by adopting an immersion precipitation phase inversion method to obtain a high-strength composite hollow fiber forward osmotic membrane; the film making process is simple; the water flux, the selectivity, the hydrophilism, the performance stability and the service life of a membrane are improved by an organic and inorganic blending membrane making method.