Due to its high carrier frequency, large bandwidth and rich spectral information, terahertz waves have been widely concerned for their potential in high-speed communication, molecular detection, and biomedical imaging. Terahertz modulator is a key device in terahertz detection system, but the currently reported modulators cannot have the characteristics of high efficiency, high speed and low insertion loss at the same time. Therefore, an electronically controlled terahertz modulator based on a GaAs Schottky diode combined with a surface plasma gate array structure is proposed and designed. The device superimposes the electric field enhancement effects of the resonant cavity and the metal gate array on each other, which significantly improves the modulation performance of the device and achieves multi-frequency modulation in the range of 0.4 to 1.4 THz with a maximum modulation depth of about 80%, insertion loss lower than 10 dB, and modulation speed greater than 100 kHz.