The invention relates to a coaxial helicopter capable of controlling flying speed change completely by buttons. The coaxial helicopter comprises a machine body (1), a tail rotor direction expansion piece (14), a flywheel gear (15) and a tail rotor distance expansion piece (21); two rotor wings are arranged on an engine output shaft in an engine cabin at the upper layer of the machine body (1) and rotate to run in reverse directions by virtue of gears, a front-back inclined expansion piece (2) and a left-right inclined expansion piece (3) are arranged on a fixing disc on a sheath of the engine output shaft, and the fixing disc is connected with an inclined movable disc; and the distance, direction and angle of the tail rotor direction expansion piece (14) are controlled by the buttons, and the lower part of the tail rotor direction expansion piece (14) is connected with a tail rotor angle rod (17) so that the distance and angle of a tail rotor (26) are switched and changed. Besides the existing coaxial rotor wing distance reversion technique, especially an original technique of randomly changing tail rotor angle as an important pushing and pulling power, the coaxial helicopter capable of controlling the flying speed change completely by the buttons, disclosed by the invention, is an ideal air transportation tool for transporting relief materials for persons in disaster area at the highest speed.