Abstract: A partial model of a reversed tainter valve for shiplock described in this paper is used in displaying flow patterns and structures behind the valve with computer image processing system composed of 386 microcomputer, VP32 image board and CCD image sensor etc. In turn, we have got a clearer image spectrum of flow behind the valve, given a formula to estimate length of backflow region under steady flow conditions and derived contraction coefficients for various openings, with the aid of flow patterns disply and measurement of contraction coefficients.