The invention provides a positioning installation clamp which is used for clamping a cylindrical capacitor. The positioning installation clamp comprises a clamping part and a positioning installation part. The clamping part wraps and clamps the cylindrical external side wall of the capacitor. The positioning installation part is arranged on the clamping part and used for installation and positioning of the clamped capacitor. The clamping part is arranged to be an elastic clamping part used for elastically clamping the cylindrical external side wall of the capacitor. After the capacitor is installed on the positioning installation clamp, the capacitor is clamped via an elastic structure so that accuracy of the position of the capacitor after being fixed by the positioning installation part can be guaranteed. The positioning installation clamp is arranged, and the capacitor is effectively limited by the clamping part of the elastic structure. Installation of the positioning installation clamp is easy to realize via arrangement of the positioning installation part so that the cylindrical capacitor is easy to install, and effective installation limiting is also achieved. The invention also provides an electric appliance box with the cylindrical capacitor.