An exhaust gas purification device may deactivate at least one of cylinders to supply a gasoline particulate filter with sufficient air according to a driving condition of a gasoline engine, and a control method thereof and a control method thereof may include comparing a pressure difference of the gasoline particulate filter with a predetermined value, determining a cylinder that may be to be deactivated when the pressure difference may be larger than the predetermined value, regenerating the gasoline particulate filter by supplying it with air through the deactivated cylinder, determining whether the engine may be in an over-run condition during the regeneration process, and returning to a general driving condition in a case that the engine may be in the over-run condition.