A disposable blood sampler for a blood braid of a blood bag includes a blood taking needle cannula, a threaded cannula, a blood braid clamp, a connecting pipe, a needle inserting sheet and a blood braid. The blood taking needle cannula includes a tubular threaded structure at both ends, a bottom port of the threaded cannula is connected with the blood taking needle cannula, and an upper port of the threaded cannula includes symmetrically distributed clamping slots extending to a middle lower part of the wall. Grips are arranged on the outer wall surface of the blood braid clamp, and the blood braid clamp is arranged in the threaded cannula. The grip is arranged outside the clamping slot, and the connecting pipe is directly inserted into the upper port. An inner cavity in which the needle inserting sheet is placed is arranged inside the inner part of the connecting pipe.