The invention discloses a dustproof mouth mask with good sealing performance. The mouth mask comprises a mouth mask body, ear hanging ropes penetrate through the mouth mask body, and the edge of the periphery of the mouth mask body can be contracted by pulling the ear hanging ropes; a nose groove which protrudes outwards is formed in the middle of the upper end of the mouth mask body, a pluralityof tight suction cups are uniformly arranged at the peripheral edge of the side wall of the inner side of the mouth mask body, and the tight suction cups are made of latex materials; a triangular jawnotch is formed in the middle of the lower end of the mouth mask body, and a purification breathing opening is formed in the mouth mask body; the purification breathing opening is provided with a particle filtering layer, and the mouth mask body comprises an inner layer and an outer layer; an air outlet is formed in the joint between the inner layer and the outer layer of the two ends of the mouthmask body, and a flow channel is formed between the inner layer and the interior of the outer layer. The dustproof mouth mask can well solve the problem about the sealing performance of the upper endof the mouth mask, and the situation that all exhaled air overflows from the upper end and causes lens fogging is avoided; meanwhile, the exhaled air can be well discharged from other directions, andthe exhaled air can be prevented from being left in the mouth mask.