With micro-pulse lidar (MPL) data, the max mixing height (MMH) in the summer of Naqu is retrieved by gradient method. With radiosonde data (twice daily at 08:00 and 20:00) and max potential temperature of Naqu in the corresponding date, MMH is retrieved by parcel method. The intercomparison between MMHs from the different data shows that the result from 08:00 radiosonde data consists well with MPL results, with correlation coefficient 0.85, root-mean-square error (RMSE) 0.30 km, mean absolute error (MAE) 0.25 km, and the t-test (0.95) passed. But the result from 20:00 radiosonde data has larger deviation from MPL results, with the correlation coefficient 0.84, RMSE 0.67 km, MAE 0.54 km and failed in the t-test. Deviation analysis shows that some factors such as the residual mixing layer in 20:00 soundings, some local weather process before the 20:00 launch time and the temporal-spatial variation of the mixing height induced by the thermal convective bubbles or/and the entrainment process may cause the inconsistency in the results. All above lead to the non-availability of the 20:00 radiosonde data in retrieving the mixing height. The character of the diurnal variation of the potential temperature profile will also affect the accuracy of retrieval result, which would produce a higher height from 08:00 data, and some statistical corrections should be used to improve the result.