An image forming apparatus to reduce time required for printing consecutive pages of printing data and an image forming method thereof. The apparatus includes a data processing unit for performing a pre-printing process of received printing data in single page units. A printing unit for printing a first page and performing an after-printing process when there is not a second page or when the pre-printing process of the second page is not complete. A controlling unit for controlling the printing unit to end the after-printing process for the first page when the pre-printing process of the second page is complete.