Currently in the whole world, Beypazari trona solution project is the largest mining engineering with the methods of solution mining and intersected well drilling. Due to the geological condition changes and abnormal earth magnetism behavior, some abnormal deviations happened with the MWD device. An in-situ probe calibration work is designed and preformed so as to find what influences the probe measurement precision. The calibration results show the assembly condition of MWD probes greatly contributes the deviation of measurement, thus some measures are necessarily taken to prevent from such errors in the well drilling construction.