Abstract: The characteristics of configuration and operating principle of Collimated Abrasive Water Jets (CAWJ) and particle accelerating equation with energy loss in the collimating pipe are analyzed. Theoretical and experimental results show that particle speed of CAWJ retains constant basically as the pipe length is in the range of 0.4m to 3m. There is all optimal relationship between the parameters of the collimating pipes and abrasives. The application of CAWJ for cutting and breaking is discussed in this pape...