The basic principle of particle image velocinmetry(PIV)is described.When a PIV image is an-alyzed by the method of auto-correlation,there is a direction ambiguity of 180~0 in velocity measurement.The problem can be solved by using"Image Shifting Technique",but this makes devices much complicat-ed and difficult to control.A new arrangement of 2-CCD(Charge Coupled Device)fully digitized PIV sys-tem,which can also solve the problem successfully,is introduced in the paper.As an example of applica-tion of the system,an experimental result of flow field around a horizontal cylinder in wave is presented.