The invention belongs to the technical field of preparation of selenium-containing polymers, and discloses a method for preparing polyselenourea / polyselenoamide through multi-component polymerizationof elemental selenium, isonitrile / alkyne and amine. The method comprises: carrying out a reaction on elemental selenium, a binary triple bond compound and a diamine in an organic solvent under an inert atmosphere, and subsequently treating to obtain a selenium-containing polymer, wherein the binary triple bond compound is binary isonitrile or binary alkyne, and the selenium-containing polymer is polyselenourea or polyselenoamide. According to the present invention, the method has characteristics of mild reaction conditions, high efficiency, energy saving, no catalyst, no by-product generation,atomic economy, green chemistry, low monomer toxicity, high atom utilization rate and high yield (more than or equal to 90%); the group has strong tolerance, and a variety of functional groups can beintroduced into the monomer; and the polyselenourea / polyselenoamide is stable, and can be degraded under specific conditions.