A lever is the main structure of catapult that appeared in China, and the structure of the lever is constructed on a frame(data). At the bottom of the frame, an axis is set up for the beam which can rotate vertically through a wide arc. The distance from two vertices to the axis (fulcrum) is at a ratio（unbalanced）, that a spoon-like structure or a sling will be put on the vertex of the longer side. While, string and yard will be installed on the shorter side.

When using the catapult, the longer side of the beam will be pulled down to load the projectile. To sustain the mass and to protect the beam not to break during the swing, some will]increase the number of beams to [strengthen the tenacity/ reinforce the structure. A catapult in China was found with a beam that combines 7 wooden sticks.

On the other hand, a counterweight catapult has the counterweight installed on the shorter side of the beam. There are two launching methods using two different forces. The first method is using human force that a group of people pulls the string from the beam is that the shorter side or the longer side, then walks backward or forward: do you mean back and forth to let the beam swing and throw the projectile.