The stairs being loaded can be divided into single run stairs, double run stairs, and multiple run stairs by flight. The plane shape of the flight includes straight, polyline and curve. The single stair is the simplest, suitable for buildings with low storey height; Double running stairs are the most common, including double running straight up, double running zigzag, double running folding (parallel), etc., which are suitable for general civil and industrial buildings; Three running stairs have three fold type, T-type, split type, etc., which are mostly used in public buildings; The scissor staircase system is composed of a pair of double running parallel stairs in opposite directions, or a pair of overlapping but disconnected single running straight stairs. The cross section is in the shape of scissors, which can pass through more people at the same time and save space; The spiral staircase is supported on the middle column with fan-shaped steps. Although it is not comfortable to walk, it saves space and is suitable for places with less people and infrequent use; Circular, semicircular and arc-shaped stairs are supported by curved beams or curved plates. The steps are slightly fan-shaped. They are colorful, lively and decorative, and are suitable for public buildings.