A screw expander, comprising: a main body, having a high pressure region, an expansion region, and a low pressure region; at least an expansion screw, disposed at the expansion region and having an air inlet end and an air outlet end, wherein the air inlet end is connected to the high pressure region, and the air outlet end is connected to the low pressure region; and an adjusting component (130, 130'), covering the expansion screw, and adapted to move relatively to the expansion screw to change an opening area of the air inlet end or an opening area of the air outlet end, such that a pressure of an air exhausted from the air outlet end is adjusted, wherein an end of the adjusting component has a recess (130a, 130a'); when the adjusting component moves to a first position, the recess (130a, 130a') is aligned with the air inlet end or the air outlet end to increase an opening area of the air inlet end or an opening area of the air outlet end; when the adjusting component moves to a second position, the recess (130a, 130a') is dislocated with the air inlet end or the air outlet end to reduce the opening area of the air inlet end or the opening area of the air outlet end, characterized by a control module configured to sense pressure of the expansion region and pressure of the low pressure region, and thus being configured to control movements of the adjusting component, wherein the adjusting component has a straight channel perpendicular to the main axis of the adjusting component and connected to or positioned within the expansion region, the control module senses the pressure of the expansion region through the channel, and a distance of the channel and the air outlet end is shorter than a distance of the channel and the air inlet end. a main body, having a high pressure region, an expansion region, and a low pressure region; at least an expansion screw, disposed at the expansion region and having an air inlet end and an air outlet end, wherein the air inlet end is connected to the high pressure region, and the air outlet end is connected to the low pressure region; and an adjusting component (130, 130'), covering the expansion screw, and adapted to move relatively to the expansion screw to change an opening area of the air inlet end or an opening area of the air outlet end, such that a pressure of an air exhausted from the air outlet end is adjusted, wherein an end of the adjusting component has a recess (130a, 130a'); when the adjusting component moves to a first position, the recess (130a, 130a') is aligned with the air inlet end or the air outlet end to increase an opening area of the air inlet end or an opening area of the air outlet end; when the adjusting component moves to a second position, the recess (130a, 130a') is dislocated with the air inlet end or the air outlet end to reduce the opening area of the air inlet end or the opening area of the air outlet end, characterized by a control module configured to sense pressure of the expansion region and pressure of the low pressure region, and thus being configured to control movements of the adjusting component, wherein the adjusting component has a straight channel perpendicular to the main axis of the adjusting component and connected to or positioned within the expansion region, the control module senses the pressure of the expansion region through the channel, and a distance of the channel and the air outlet end is shorter than a distance of the channel and the air inlet end.