The invention relates to an electric connection device and a plug and socket thereof, wherein the plug is provided with a square plugging bolt which is provided with a first grounding electrode and a square first power electrode; the socket is provided with a plugging bolt hole, the wall of the hole is provided with a second grounding electrode and a second power electrode, the lower edges of thefirst grounding electrode and the first power electrode are provided with first arc chamfers; the upper edges of the second grounding electrode and the second power electrode are provided with secondarc chamfers, the first arc chamfers and the second arc chamfers fit with each other when inserted into each other so as to facilitate the electrodes to insert, the longer edge of the first power electrode is inserted in the socket for contact and conduction, and the shorter edge of the first grounding electrode is inserted in the socket for contact and conduction. Therefore, the electric connection is more reliable and the operation is easier.