Abstract: Based on NCEP/NCAR daily reanalysis data, the position variation of the western Pacific subtropical high (WPSH) in June 2005 and its relation to diabatic heating are analyzed using the complete vertical vorticity equation. The results show that the position variation of WPSH is associated with the diabatic heating in subtropical areas. In comparison with June climatology, there were strong heating to the north side of WPSH and relatively weak ITCZ convection to the south side in June 2005. Along with the northward movement of WPSH, the convective latent heating extended northwards from its south side. The heating to the west of WPSH was generally greater than that inside of the WPSH, and each of significantly enhancements in the heating corresponded to a subsequent westward extension of WPSH In mid-troposphere, the vertical variation of heating rates to the north of WPSH was basically greater than the climatology, which is unfavorable to the northward movement of WPSH. On the other hand, the vertical variation of heating to the south of WPSH was mainly less than the climatology, which is favorable to the anomalous increase of anti-cyclonic vorticity, leading to the southward retreat of WPSH. Before the westward extension of WPSH in the late June 2005, the vertical variation of heating rates to the west (east) of WPSH was largely higher (lower) than the climatology, which is in favor of the increase of anti-cyclonic (cyclonic) vorticity to the west (east) of WPSH, inducing the subsequent westward extension of WPSH. There were similar features in lower troposphere. As a result, the heating to the north and south, the east and west of WPSH worked together to make the WPSH extend more southwards and westwards in June 2005, which is in favor to maintain the rainbelts in South China.