Labyrinth path drip irrigation emitter is one of the predominant drippers. Based on the exact test to the geometry parameters of three representative sawtooth-labyrinth paths, the mechanism of pressure losses in the flow path was studied by the smooth pipe turbulence theory and CFD （computational fluid dynamics）technology of flow regime. The mechanism of pressure losses in sawtooth-labyrinth path couldn't be explained with smooth pipe turbulence theory. The pressure was descending with linearity rules along the flow path, and the head losses was equaled. The friction coefficient reduced with the pressure increasing, and it was stabilized to a value soon. The flow regime is turbulent within the sawtooth-labyrinth paths the pressure zone higher than 50 kPa, and it is possible that the transformation behaviors of the flow from laminar flow or smooth turbulent into turbulent flow were existed. 