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 4.9×10⁸~6.1×10⁸ Pa with average 5.4×10⁸ Pa, corresponding to 16~20 km with average 18 km in depth. Combing with previous studies, we suggest that the emplace depth is 17~19 km, and we can presume that crustal thickness of South China in the Indosinian period was likely ≥50 km, 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.