In this study, first arrival P-wave of micro-earthquakes with magnitude less than 4 is used to calculate a 3-D crustal velocity structure of Dehdasht region. For this purpose, waveform data from 116 stations which were recorded between September 20th, 2016 and July 2nd, 2017, was used. Of the total earthquakes recorded, more than 1000 events were selected for the tomography so that the results would have the least effect of human mistakes (e.g. phase picking) or computational errors (e.g. location uncertainties). The tomographic results show three main tectonic characteristics including high-velocity anomalies in west, and two low-velocity anomalies in Dehdasht basin and southeast of Dehdasht city. Furthermore, most of known faults clearly appear around the low-velocity anomalies. Our tomographic maps show that the Dehdasht region cover by a layer with thickness of ~4 km which is overlay the hard bedrock with constant velocity.