Abstract: The axial and radial distributions of the superharmonic component (linear summation of the amplitudes of the third,fourth and fifth order components) radiated from a piston source are studied in theory as well as in measurement.Dependences of the amplitude and the beam pattern of the superharmonic component on the source sound pressure and the propagation distance are discussed.Results demonstrate that at the appropriate source acoustic pressure amplitude and propagation distance,the amplitude of the superharmonic component is larger than that of the second harmonics,and the-3 dB beam width of the superharmonic component is reduced to 59% and 77% of those of the fundamental wave and the second harmonic,respectively.Superharmonic imaging is made for biological tissues and compared with the results from fundamental and second harmonic imaging.Results indicated that the superharmonic component can improve signal-noise-ratio and resolution in ultrasonic nonlinear imaging.