Muscovite is a common mineral in peraluminous granites, it could be a mineral barometer to constrain the emplacement depth of peraluminous granites. Chemical compositions of muscovite from the Jintan two-mica granite are determined using electron microprobe. According to the calculation for the crystallization pressure of the muscovite, the pressure of emplacement of the Jintan pluton is 4.9×108 Pa~6.1×108 Pa with average ~5.4×108 Pa, corresponding to 16~20km with average ~18km in depth. Combing with previous studies, we suggest that the emplace depth is 17~19km, and we can presume that crustal thickness of South China in the Indosinian period was likely ≥50km, but it may be denudated because of extensive weathering in the Yanshanian period, which can be a new explanation for the lacking Indosinian volcanic rocks in South China.