The invention discloses a portable atmospheric particulate dilution channel sampler. The sampler comprises a diluting system and a sampling system, wherein the diluting system comprises a primary diluting bin, a secondary diluting bin and a remaining room which are connected in sequence, a particulate inlet of the primary diluting bin is connected with a sampling probe by a sampling tube, the primary diluting bin is provided with a primary clean air guide inlet, the secondary diluting bin is provided with a secondary clean air guide inlet and a secondary bypass outlet, and the remaining room is provided with a sampling hole and a condensate collecting hole; the sampling system comprises a plurality of sampling branch tubes connected with the sampling hole and a sampling header connected with all the sampling branch tubes, each sampling branch tube is provided with a sampling cutter, a sampling flow control valve and a sampling flow meter, and the sampling header is provided with a sampling pump. The invention also discloses a portable atmospheric particulate dilution channel sampling method. According to the invention, the dilution ratio of atmospheric particulates and the sampling precision are improved, and the practicability is high.