The invention discloses a method for preparing polymer based on a semi-continuous material feeding method. The method for preparing the polymer based on the semi-continuous material feeding method comprises the steps: mixing water-soluble monomers, a chain transfer agent, an initiator and water uniformly for a reaction so as to obtain a polymer solution, mixing an oxygen-removed part of monomers,an initiator, water and the polymer solution, introducing argon gas for oxygen removal, performing heating, adding the remaining monomers to a container through a micro-injection pump for a feeding time of 90-150 min so as to obtain a soap-free polymer emulsion after completion of material feeding, performing freeze-drying, and performing precipitation, still standing, suction filtration and drying so as to obtain the polymer. The high-solid content soap-free emulsion with a maximum solid content of 60% can be prepared by using the semi-continuous material feeding method, and a new idea for preparing a high-solid content emulsion is provided; the polymer emulsion is formed in situ during the reaction so that use of emulsifier and residual of the emulsifier in the product can be avoided, and meanwhile the homopolymer which is synthesized in the first step needs no post-treatment, and can be directly applied to emulsion polymerization in the second step so as to obtain the polymer, so that the operation steps are simplified greatly.