A new type of liquid propeller-double-blade propeller is discovered and its performance parameters are derived by means of kinematics analysis of the blade and loads applied on the blades.An example is given for comparing the performance parameters of the double-blade propeller with a single-blade propeller’s in the same mechanism size using the derived equations.The results demonstrate that the propulsion force of the double-blade propeller is increased in frequency but decreased in fluctuation

and the lateral force is reduced in magnitude but increased in frequency

and the propulsion efficiency in theory is about 66%.