Within natural ecosystems, land exploitation and environmental changes in particular vegetation and land use affect hydrological Reponses like flooding, erosion rate and sedimentation in tur impose adverse socioeconomically damages. The most important outcomes for land use change on basin hydrology are changes would occurred in peak discharge, total runoff volume, water quality and hydrological balances. The present research is aimed to apply computer-based model HEC-HMS to simulate flow hydrograph for Shiraz khoshk river basin and to investigate the ground water level using evaluation indices and comparing the results. Results from calibration and validation of HEC-HMS model, showed suitable correlation to measured flow discharge data in basin output. Values for indices for model efficiency in the present research involved Nash-Satklif index, simulation variance coefficient, model bias in flow volume estimation, error percent in peak flow, coefficient of determination, weighted determination coefficient and least square error mean were in acceptable level. It can be concluded that applied model presents good estimate on maximum peak flow and time to peak and it has poor performance in estimating flow volume and descending branch prediction. Flow peak ratio in 2011 compared to 1987 was 10.3 and 12.3 in 100 and 2 years return period’s respectively. Time to peak flood occurrence in model HEC-HMS for different scenarios and various return periods did not differed significantly. Flow volume ratio in 2011 compared to 1987 have increased about 10.7 and 9.1% respectively. Keywords: Shiraz khoshk river basin, HEC-HMS, floatability, land use