Abstract: Solutions have been put forward to solve the problem that the size of the existing MWD inclinometer is too large for the measurement of rod with a diameter of 50 mm and the calibration time is too long. Firstly, a small size storage MWD inclinometer with a diameter of 25 mm was designed by using MEMS sensors; secondly, the error of MEMS sensors was compensated by ellipsoid fitting calculation method, and the inclinometer was calibrated with 20 reference points through the spatial coordinate transformation; finally, the data before and after the calibration of the inclinometer were tested and compared.The result showed that the water flow cross section area of the designed MWD inclinometer reaches 471 mm², the calibration time is reduced to 15 minutes, from 4 hours to 5 hours, the root mean square error of tilt angle decreases from 0.57° to 0.08°, and the root mean square error of azimuth angle decreases from 3.90° to 0.85°, which is suitable for the storage MWD measurement of rod with a diameter of 50 mm.