Abstract: After analysis on air lock check formula, given are two solutions to air lock problem; ①make the oil product with large H pass through the peak point of unloading arm by changing unloading sequence; ② adjust the arm to reduce its distance to tank bottom. Accordingly, integral, layered unloading arm is designed. Welded to road tanker and with some operation executed on ground, the new unloading arm is easy to operate, safe and reliable. A strict air lock check is made for the working process of an integral, layered unloading arm which is located in Chongqing, one of the most hot areas in China. The check result shows that air lock can be avoided even in adverse conditions.