X-rays have high photon energy, which results in a significant penetration depth in ZnO materials. Therefore, in order to detect X-rays effectively, it is necessary to prepare ZnO films with a thickness of micrometers or hundreds of micrometers. In this paper, a 14.85 μm-thick ZnO film was rapidly prepared by electrochemical deposition method. The experimental results show that the deposition potential and electrode material have a significant effect on the deposition rate and surface morphology of ZnO films. With increasing the deposition potential, the morphology of ZnO changes from hexagonal columnar to lamellar structure. When the potential is too high, a large amount of hydrogen is generated, resulting in an increase in the number of holes in the film that prevent it from forming. When using metal Pt as the anode electrode, the solution will gradually acidify, resulting in the dissolution of ZnO as it is deposited, and when the rates of the two coincide, the ZnO film thickness will no longer increase, making it unsuitable for growing ZnO thick films. In contrast, when using metal Zn as the anode electrode, the pH of the solution remains essentially unchanged, which is more suitable for growing ZnO thick films. A ZnO thick film of 14.85 μm was grown for 1 h using metallic Zn as the anode electrode with a deposition potential of 0.65 V and an electrolyte concentration of 0.4 mol/L. When biased at 5 V, the ZnO thick film based detector has been shown to achieve a responsivity of 66.8 μC·Gy-1·cm-2 to X-rays with an accelerating voltage of 40 kV.