Abstract: Design principle and method of a waterpower test instrument for composite geomembrane were described.Waterpower test for com posite geomembrane was realized by linking master computer to slaver 89C52 singl e-chip computer with RS-485 bus.Single-chip computer could control pressure a nd measure hydraulic pressure,water volume and time.The master computer could pr o cess collected data,print reports and draw curves as well as display and save th e result through communicating all slaver computers which improve the precision and efficiency of measurement.Some factors affecting the precision of measuremen t were also discussed.