The invention discloses a light calcined magnesium oxide retarder based on composite vitamins, the light calcined magnesium oxide retarder comprises the following components in parts by weight: 40-70parts of vitamin c, 10-20 parts of vitamin b1, 10-20 parts of vitamin b2 and 10-20 parts of vitamin b6, the light calcined magnesium oxide retarder is prepared by the following steps: 1) grinding vitamin tablets into powder; and 2) uniformly mixing the powder at normal temperature according to the proportion to obtain the required magnesium oxide retarder. The vitamin magnesium oxide retarder provided by the invention provides a new idea from a biological drug angle for preparation of a cement-based material additive, the preparation process is simple, safe and non-toxic, and the initial and final setting time can be remarkably prolonged.