The present invention relates to an unmanned helicopter. The unmanned helicopter comprises a fuselage. Two arms are respectively disposed on each of two sides of the fuselage. One end of each arm is connected to the fuselage, and the other end of each arm is provided with a rotor having a motor. The unmanned helicopter is characterized in that: the four arms are grouped into a front group and a rear group, two arms in each group are disposed symmetrically along the axis of the fuselage, the fuselage is movably connected to each arm, an angle between a length direction of any one of the two arms in each group and a corresponding rotation axis is an angle r, an angle between the rotation axis and a horizontal surface of the fuselage is an angle a, and an angle between a projection line of the rotation axis on the horizontal surface of the fuselage and the axis direction that extends outward the fuselage is an angle b. By ingeniously selecting values of the angle a, the angle r and the angle b, the structure of the unmanned helicopter in a folded state is very compact, thereby effectively saving space.