We developed a novel Thick Gas Electron Multiplier (THGEM) film based on simulation results. With new substrate material and homemade industrial PCB technology, the film has good stability, the gain of monolayer reaches 2×10 4 and the working voltage range exceeds 150V. Although the detection efficiency of monolayer THGEM detector in high-energy gamma rays was only 0.2%, we measured high-energy gamma dose rates in the range of 0.3μGy/h to 8Gy/h ( 137 Cs and 60 Co) by switching between counting mode and current mode. The detector was not saturated at all even at very high dose rates in current mode. This study indicates that THGEM detector has a broad application prospect in the field of high-energy gamma detection, especially in the extremely high dose rate gamma radiation field, such as nuclear power plant radiation leakage accident.