The invention belongs to the field of high polymer chemistry, and in particular relates to a soft polyurethane foam material and a preparation method thereof. The soft polyurethane foam material is especially suitable for being taken as a cushion material of an environment-friendly automobile seat. The soft polyurethane foam material is prepared via a chain extension reaction of polyisocyanate and polyether polyol system materials, wherein the weight ratio of the polyether polyol system materials to the polyisocyanate is 100 to (35-55). The soft polyurethane foam material and the preparation method thereof are of a polyether polyol system material formula and a relevant matching process which are specially applied to 36 station foaming production lines of Hennecke Company and can comprehensively meet the automobile standard of modern enterprises as well as realize the batch production of the soft foam material for the automobile seats. Especially, aldehydes (formaldehyde/acetaldehyde/acraldehyde) in VOC indexes of the soft polyurethane foam material are not detected (ND). Thus, the soft polyurethane foam material can meet strict requirements of the automobile industry in future on environmental friendliness indexes, thereby having the perspectiveness.