The invention relates to a quantitative sampling device which comprises a sampling cavity through which a mud sample passes, a sampling inlet formed in the lower part of the side wall of the sampling cavity and a sampling outlet which is formed in the upper part of the side wall of the sampling cavity and is connected to a suction pump, wherein the mud sample enters the sampling cavity through the sampling inlet; the sampling inlet comprises a plurality of sampling holes; the sampling holes comprise small-hole sections and large-hole sections; the large-hole sections are close to the interior of the sampling cavity; and the suction pump is used for sucking the mud sample from the sampling outlet. The quantitative sampling device disclosed by the invention can realize automatic cleaning in working when the collected mud sample is filtered, so that continuous and constant flow of the mud sample can be guaranteed.