The models of jetpipe and deflectorjet hydraulic amplifier are very important and necessary for the simulation, design and application of the jettype electrohydraulic servovalve(including jetpipe servovalve and defelctorjet servovalve).Although there is no accurate mathematical model to describe their performances, a large number of approximate models are available. In order to provide a theoretical help for the design and simulation of the jettype electrohydraulic servovalve, six models are introduced in this paper, and the application conditions of these models are also introduced.