The invention discloses a capacitive series direct current magnetic bias isolation grounding device for a neutral point of a power transformer. The device comprises an isolation device and a magnetic bias monitoring device, wherein the isolation device comprises a blocking capacitor C, a voltage limiting protector FR connected in parallel with the blocking capacitor C, a high-speed bypass switch HSD and a bypass switch controller Kzl; the online magnetic bias monitoring device comprises an alternating current mutual-inductor Ta1, an alternating current and direct current transducer Ta2, a digital monitoring device Kz2, a communication terminal TX connected with the output end of the digital monitoring device Kz2 and an isolation transformer GT connected with the bypass switch controller Kz1 and the digital monitoring device Kz2 respectively. According to the device, by a zinc oxide nonlinear resistance voltage limiting protector component and a zero-crossing closing technology-based vacuum circuit breaker, the voltage grade of the blocking capacitor C is lowered, the reliability and the anti-short-circuit impact capability of the device are improved, the maximum anti-short-circuit impact current can reach 125kA, and the device can be used for neutral point grounding circuits of high-voltage, ultra-high voltage and even extra-high voltage large-sized or giant transformers; the noise of the transformer is effectively lowered, and the temperature rise of the transformer is inhibited.