The research and development of digital hydraulics technologies are developed rapidly during the past years. Many new concepts are put forward and some of them are got into application. This thesis reviews the relevant concepts and theories of the digital hydraulics at first, for instance the difference between continuous signal and numerical signal, basic components of digital hydraulics. And then elaborate on/off valve which includes performance of behave, different connection methods such like serial connection, parallel connection. Thirdly introduce an important concept that switching technology and analysis different branches for example PWM, PFM, DFCU. Besides, switching converter are also discussed. Next, the new manufacture process that laminated manifold valve are explained.