Silicon-based electro-optic modulators are the key devices in integrated optoelectronics.Integration of the graphene layer and the photonic crystal (PC) cavity is a promising way of achieving compact modulators with high efficiency.In this paper,a high-quality (Q) acceptor-type PC nanocavity is employed to integrate with a single-layer graphene for realizing strong modulation.Through tuning the chemical potential of graphene,a large wavelength shift of 2.62 nm and a Q factor modulation of larger than 5 are achieved.A modulation depth (12.8 dB) of the reflection spectrum is also obtained.Moreover,the optimized PC nanocavity has a large free spectral range of 131.59 nm,which can effectively enhance the flexibility of the modulator.It shows that the proposed graphene-based PC nanocavity is a potential candidate for compact,high-contrast,and low-power absorptive modulators in integrated silicon chips.