An optical terahertz modulator based on graphene/boron nitride 2D heterostructure coated silicon was studied in this paper. The static and dynamic modulation of THz wave were tested respectively with a 808 nm laser by using the terahertz time-domain spectrum system and a terahertz wave dynamic test system independently built by the laboratory. When the laser power is increased from 0 to 500 mW, the average transmittance through the terahertz modulator decreased from 58% to 13% with maximum modulation depth of 76% (500 mW). The maximum modulation speed obtained by the dynamic modulation test is 15 kHz (100 mW). The experimental results show that the modulation depth and speed can be obviously enhanced by graphene/boron nitride 2D hetrostructure in contrast to the single-layer graphene coated silicon.