A calibration memory control method of an ECU connected to an external calibration device may include receiving a download command from the external calibration device, checking a sub reference page corresponding to the download command, determining whether a sub working page corresponding to the checked sub reference page is allocated, allocating the sub working page corresponding to the checked sub reference page to a RAM region upon determining that the sub working page is not allocated, and copying data stored in the checked sub reference page to the allocated sub working page. As such, according to the present invention, restrictive memory resources may be efficiently used for calibration.