The invention, belonging to the field of building technology, relates to a building body with a heat preservation layer and a construction method thereof; the building body with the heat preservation layer is provided with a heat preservation layer at the outer surface of a wall basal body, the heat preservation layer comprises heat preservation plates arranged at intervals in longitudinal and transverse directions, a flexible or elastic heat preservation strip and a positioning member; the construction method thereof comprises the steps: well pre-rolling reinforced bar structures and construction formworks of beams, posts or walls, positioning the heat preservation layer at the inner surface of a construction formwork, then pouring concrete and removing the construction formwork, or directly adhering the heat preservation layer to a peripheral protective part of the masonry to reinforce overall performance of the heat preservation layer of the entire building; the invention has the advantages of short construction period, long service life of heat preservation systems, high comprehensive cost performance, extensive suitable scope, etc.