A multi-thread processor and a method of controlling a multi-thread processor are provided. The multi-thread processor includes at least one functional unit; a mode register; and a controller configured to control the mode register to store thread mode information corresponding to a task to be processed among a plurality of thread modes, wherein the plurality of thread modes are divided based on a size and a number of at least one thread that is concurrently processed in one of the at least one functional unit, allocate at least one thread included in the task to the at least one functional unit based on the thread mode information stored in the mode register and control the at least one functional unit to process the at least one thread.