In order to investigate the influence of soil moisture heterogeneity on the convective initiation stage of a mesoscale convective system over the Tibetan Plateau，an typical case of mesoscale convective system，developed from an isolated convective initiation process over the Tibetan Plateau on 10 August 2022，is studied by observational analysis and numerical experiments using satellite remote sensing data，cloud-to-ground lightning observations and reanalysis data. The results are as follows：（1）Under weak synoptic-scale forcing，the convective initiation stage of the mesoscale convective system occurred at 06:00（UTC，the same as after）. The convective cloud then moved northeastward and intensified through merging clouds，accompanied by lightning activity during the development of the mesoscale convective system.（2）Based on the mesoscale numerical model WRF， we simulated the surface convergence in the southwestern dry zone formed by surface thermal forcing，as well as the development and intensification process of the updrafts caused by the surface convergence until the formation of the convective initiation with a moving direction along the soil moisture gradient. At convective initiation time，the low-level atmosphere over the convective initiation location was in a dry adiabatic state with a CAPE （CIN）of 946. 5 J·kg-1（0 J·kg-1）. 2 m air temperature reached the convective temperature 1h before the occurrence of convective initiation，when the height of the planetary boundary layer was higher than the level of free convection. The convection then strengthened rapidly.（3）The results of the sensitivity experiments show that the removal of the soil moisture inhomogeneity weakened the intensity of the convection and shifted the position of the convective initiation westward，which is related to the fact that the soil moisture inhomogeneity changed the atmospheric dynamical，thermal and moisture conditions before the occurrence of the convective initiation. The soil moisture inhomogeneity indirectly increased the sensible heat flux of the dry zone located to the southwest of the convective initiation location by increasing the surface temperature，thus increasing the upward motion at surface before the occurrence of the convective initiation. Meanwhile，the direction of the wind field near the convective initiation location was also changed and thus increasing the convergence of the surface wind field and water vapor at the convective initiation time，which led to an increase in the intensity of the convection.（4）Under the condition of homogeneous soil moisture distribution，increasing soil moisture led to more abundant surface water vapour and stronger convergence of the surface wind field，which in turn led to an increase in the intensity of water vapour convergence and enhanced the development of convection. In addition，higher soil moisture inhibited the intensity of pre-convective initiation updraft development by decreasing surface temperature and sensible heat fluxes，which slowed the development of convection and led to a later convective initiation time.