The invention relates to a planar mask for efficiently filtering PM 2.5. The planar mask comprises a mask body used for covering the mouth and the nose of a wearer. A pair of ear hooking portions are formed on the two sides of the mask body in an extending mode and used for being hooked on the ears of the wearer. The mask body is of a three-layer structure in a stacked mode, and the three-layer structure comprises a polypropylene fiber spunbonded non-woven fabric outer layer, a superfine fiber electret melt-blown non-woven fabric middle layer and a polypropylene fiber spunbonded non-woven fabric inner layer in sequence from outside to inside. The weight per unit area of the superfine fiber electret melt-blown non-woven fabric middle layer is 20-60g/m<2>. The planar mask for efficiently filtering the PM 2.5 has the advantages of being high in filtration rate and low in choked flow, has prominent obstruction and capturing capability for the PM 2.5 and is good in breathability, low in weight, comfortable to wear and high in PM 2.5 filtering efficiency in high level. The filtering efficiency can reach up to more than 99%, the weight is low, and breathability and comfortable sensation of the mask are ensured at the same time.