The invention relates to a phosphorus flame retardant and an all water blown phosphorus containing flame retardant polyurethane foam based on the same. The phosphorus flame retardant has a structural formula represented by the formula (1). In the formula (1), R represents an alkyl group or an aryl group; n is an integer from 1 to 20; and when n is greater than 1, the R in the group (shown in the description) can be the same or different. The phosphorus flame retardant comprises reactive functional groups and can be used as polyol for preparing polyurethane foams; the density of polyurethane foams is not increased greatly, the influence on the mechanical properties of polyurethane foams is little; the raw material price is low, the cost is reduced; the preparation is carried out at a room temperature, heating is not needed, the operation is simple and convenient; based on the phosphorus flame retardant, flame retardant polyurethane is prepared, water is taken as the foaming agent, and thus the technology is environment-friendly and economic.