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The performance of CdZnTe detectors is not only influenced by the growth of crystal, but also by the quality of the interface layer between the crystal and the electrode. A model of CdZnTe detector with metal–semiconductor–metal structure is developed to investigate the effects of the interface on the space charge and electric field distribution. Atomic force microscopy, current–voltage (I–V) analysis, and energy spectra under 241Am irradiation are adopted to investigate the effects of argon (Ar) plasma treatment on the interface and performance of CdZnTe detectors experimentally. The simulation results show that the interface layer with low density of surface state and thin thickness can form a more uniform space charge and electric field distribution. Due to the decrease of voltage drop across the interface, the leakage current at 200 V of CdZnTe detector with Ar plasma treatment is reduced from 159 to 44 nA cm−2, and the full‐width at half‐maximum under 241Am is improved from 9.3% to 8.2%, as compared to conventional Br‐MeOH treatment.