The invention discloses a power input coupler, which comprises a power input end, a coaxial converter, a high-frequency ceramic window, and an output end external conductor component. The power inputend inputs power; the coaxial converter is connected with the power input end and comprises an outer conductor and an inner conductor; the high-frequency camera window is connected with the coaxial converter, and comprises a ceramic window; the ceramic window comprises a step cylindrical ceramic pipe under a room temperature condition, and the step cylindrical ceramic pipe is composed of at leasttwo cylindrical ceramic pipes with gradually reduced diameter along the power transmission direction; the an output end external conductor component is connected with the high-frequency ceramic window, and outputs the power. The power input coupler is simple in structure, low in welding difficulty, improves window intensity, and enhances the heat insulation coefficient.