The invention provides an automatic flexible crankshaft connecting line based on robots and a machining method of crankshafts. The automatic flexible crankshaft connecting line based on the robots comprises a vertically-inserting type crankshaft storing unit, and the number of stored crankshafts is increased several times; the multi-grab truss feeding robot and the truss discharging robot are arranged on two independent trusses, and it is guaranteed that interference and impacting are avoided between the robots. The machining method of the crankshafts is based on the automatic flexible crankshaft connecting line; due to the stored crankshafts in the number increased several times and the multi-grab truss feeding robot, the crankshaft carrying speed during machining is increased several times.