The invention discloses a turboshaft engine intake device and an operation method thereof. The turboshaft engine intake device comprises a central body component, a wedge component and a casing component, and is characterized in that a flexible deformable annular air chamber is embedded into the central body component, meanwhile, a wedge capable of moving in the axial direction is designed, and the profiles of the air chamber and the axial position of the wedge can be adjusted according to the working environment and the working state of an engine. When a helicopter works in unclean air environments such as the environment with dust sand, the intake system is enabled to work in a mode with high dust sand separation efficiency through increasing the height of the air chamber and moving the wedge forwards; and when the helicopter is in a cruising state, the intake system is enabled to work in a mode with high aerodynamic efficiency by reducing the height of the air chamber and moving the wedge backwards. The invention effectively solves the problem that a traditional fixed-geometry intake system cannot give consideration to both low-altitude efficient sand draining and high cruising aerodynamic performance.