Abstract: When pumping oil well flow pressure is lower than saturate pressure, annular gas is separated from oil and foamy section produces. So there's no significant surface of oil and gas. We can not get the true information of real fluid surface by echo sounder, and it causes a certain of errors to flow pressure calculation. And also it makes us have wrong production decision.Pseudo-liquid surface tester, which comes from the idea of material balance, can calculate the height of annular pseudo-gas column by testing pressure gradient and gas column of oil casingannular exhaust and resume,as well as oil and gas oportion,moisture content, gas proportion and making correction. And that is the real liquid surface of oil well. Field tests show that the errors can be 10% lower by this way than by echo testing, and it can meets the demand of liquid testing of oil well.

Key words: pumping oil well, real liquid surface, matching, material balance, flow pressure