The invention provides a three-phase phase checking device applied to power distribution network 10 kV switch cabinets and a phase checking method. The phase checking device comprises two three-phase sampling modules respectively corresponding to two ring network cabinets. The two three-phase sampling modules are respectively connected to live-line display device interfaces of the A ring network cabinet and the B ring network cabinet through connecting wire plugs of themselves. The device is provided with an analog-to-digital conversion module, and voltage analog signals collected by the three-phase sampling modules are converted into digital signals through the analog-to-digital conversion module. A central processing and calculation module calculates the digital signals so as to judge whether the three-phase voltages are identical in phase. The central processing and calculation module is connected with a display and indication module which is capable of indicating that the corresponding three-phase voltages of the two switch cabinets are consistent in phase. The device is light in weight, small in size, portable, simple and convenient to use and operate, safe and high in efficiency, and the phase checking efficiency and the phase checking accuracy of an operator are substantially improved.