A correct election of potential evapotranspiration (PET) equation is critical for water balance estimation of forest. The objective of this work was analyze the PET equations of SIMGRO model (SIMulation of GROundwater). SIMGRO model solves water balance in the unsaturated zone and the acuifer of diverse landuse covers, forest inclusively. The water consumption of the Eucalyptus dunnii was measured in a commercial forest. The weather data was measured daily and the humidity contents were measured up to 2 ms of depth monthly. The experimental sites were two: 1) old mounts, 8 years old and 2)young mounts ,2 years old. The PET equations of Makkink,Priestley- Taylor and Penman-Monteith were compared and ordered in increasing of meteorological data.requirments. The comparison of eucalyptus water consumptions with all .estimated data by the equations,were very significant in adult and young state.