In vivo electron paramagnetic resonance (EPR) tooth dosimetry can be used to estimate the absorbed radiation dose quickly and noninvasively. In this study, a magnet modulation driving device was developed for in vivo EPR tooth dosimetry. The device included a driving amplifier, a couple of coil sets generating modulation magnet field, a modulation frequency setting unit and a display unit. The driving amplifier used a switching circuit based on multi N-MOSFET H-bridge, instead of the traditional linearly analogue circuit. The amplifier had the characters of higher power capacity, high efficiency, simple structure and high flexibility for frequency setting. Experimental results showed that (1) the device could generate modulation magnet field, 0~0.9 mT in amplitude and 10~100 kHz in frequency, in the center of the two magnet poles separated more than 9 cm apart; (2) line broadening process feature of 1,1-diphenyl-2-picrylhydrazyl (DPPH) was observed with increasing modulation amplitude and radiation induced free radical signals in intact tooth. The preliminary results demonstrated that the device developed for in vivo EPR tooth dosimetry had high-efficiency and practicability.