The invention discloses a method for preparing a hollow fiber type forward osmotic membrane, which specifically comprises the following steps that: 1, a hollow fiber substrate membrane is made into a membrane component, and the membrane component is put in a membrane filtration device; 2, the residual glycerol on the surface of the membrane component is washed with water, the residual water of the membrane component is removed, and the hollow fiber substrate membrane is dried; 3, a polyamine aqueous solution is prepared and is enabled to pass through the internal surface of the membrane component, and then, the residual water on the surface of the membrane component is removed; 4, an organic solution which contains multi-acyl chloride is prepared, and is enabled to pass through the internal surface of the membrane component to react for a certain while; and 5, after the reaction is completed, the aqueous solution which contains alcohol is used to treat the membrane which is obtained from the reaction, so the hollow fiber type forward osmotic membrane is obtained. The hollow fiber composite forward osmotic membrane which is prepared by the method for preparing the hollow fiber type forward osmotic membrane has high filling rate and pollution resistance, is easy to clean, has a large effective filter area compared with components of the same size, and is suitable for a forward osmotic separation process.