[en] When the uranium reserves is determined by interpreting uranium content using gamma-logging, the ore gravity should be in the natural condition. If the ore-core has large porosity and is dewatered partially, large pore exists on the surface of the ore-core, the gravities determined by sealing-paraffin method are systematically lower. Thus, the author has proposed a calibration method to improve the measurement and taking a deposit as an example, the reasons for the surface pore and the calibrated results are analysed