Abstract: The density and distribution of neutral particles in the divertor region are very important for studying plasma physics on plasma−wall interaction. The strong magnetic field and electromagnetic environment in the divertor make it difficult to accurately measure the neutral particles density by the normal gauge. This leads to hard in−situ measurement of neutral particle density. A hot cathode ionization gauge (fast ionization gauge) diagnostic system was employed in EAST Tokamak, and experimental studies of in−situ measurement of neutral pressure were carried out. Phase-sensitive detection technology is used to detect the very weak signal in the range of 10 nA−10 μA under a strong electromagnetic environment. The fast ionization gauge was calibrated in the range of 1×10⁻³−1 Pa under a 0.35 T magnetic field, and it has a good linear relationship with the pressure. The ion current is also proportional to the filament emission current under the same pressure. Moreover, the sensitivity of the fast gauge will be significantly improved at > 0.35 T. The results show that the fast ionization gauge diagnostic system works very well in 0 −1.4 T magnetic fields, and its measurement covers the neutral pressure range of the divertor region. The fast ionization gauge meets the requirement of in−situ measurement of neutral pressure in the divertor region, which provides a powerful tool for studies on divertor physics in EAST and future fusion reactors.