The utility model discloses a respiratory gas unpowered sampler for an oil field storage tank. The respiratory gas unpowered sampler comprises a double-port barrel acquisition bottle, an L-shaped tube and a straight tube, wherein the double-port barrel acquisition bottle is connected to the vertical open end of the L-shaped tube, the transversal open end of the L-shaped tube is connected with the straight tube, the other end of the straight tube is connected with a gas collection tube, and a sealing ring for carrying out sealing connection with the respiratory port of the circular respiratory valve of the storage tank is arranged on the gas collection tube; the sealing ring is capable of expanding through the opening thereof; the L-shaped tube is connected with the straight tube through a sealing flange; a speed meter connected into the L-shaped tube and the straight tube is fixed on the sealing flange; a speed measurement probe jack is formed in the transversal tube of the L-shaped tube; an in-tube baffle is arranged in the vertical tube of the L-shaped tube, and the baffle is located below the double-port barrel acquisition bottle. The respiratory gas unpowered sampler disclosed by the utility model is high in safety, good in sealing performance, convenient to install and detach, and reliable in performance.