The invention discloses an eccentric actuator. The eccentric actuator comprises an outer barrel, upper rotary short connection, lower rotary short connection, an eccentric actuating barrel, an eccentric wedge block and a power source. The upper rotary short connection and the lower rotary short connection are connected through shaft coupler. The power source is connected to the upper rotary short connection in a sleeving manner. The power source is connected with the eccentric actuating barrel. The eccentric actuating barrel is connected to the upper rotary short connection and the lower rotary short connection in a sleeving manner. A gap is formed between the lower rotary short connection and the outer barrel. The eccentric wedge block is connected to the eccentric actuating barrel. The lower rotary short connection comprises an inner end, an outer end and a transition segment. The outer end extends out of the outer barrel. The inner end is located in the shaft coupler. The outer end diameter is larger than the inner end diameter. The transition segment is a slope. When the lower rotary short connection is not eccentric, the wedge block is located in the gap between the inner end and the outer barrel; and when the lower rotary short connection is eccentric, the wedge block is located in the gap between the transition segment and the outer barrel. According to the eccentric actuator, through controlling the lower rotary short connection to be eccentric, a drill bit connected with the lower rotary short connection can be controlled to be eccentric, and change of the direction of the drill bit is achieved so that changing of borehole trajectory can be achieved.