Step screen is a fully automatic debris removal equipment. Its operation mode can be actuated by preset level differential detector or time relay. The screen bars are crisscross arranged with fixed bars and movable bars to form the step configuration. When the level different reached the preset value caused by accumulation of debris on bars or time relay actuated, the movable bars switched on and started its convolute moving. Every convolute moving of movable bars elevated the debris up to the nearest upper layer of fixed bars. Most moisture will be dropped into the channel when the debris has been elevated from water. The debris on the highest layer of fixed bars will be ejected to debris bin or conveyor automatically by its convolutely moving. This unique equipment can be used in any inlet of waste water treatment plant for debris removal.