The invention discloses a method and a device for internal memory initialization. The method comprises the steps of judging whether the number of bytes to be filled is greater than a preset byte number or not, wherein the preset byte number is a natural number which is greater than 1; if so, continuously filling the preset byte number of bytes to initiate an internal memory. By using the method and the device for internal memory initialization, the problems that the internal memory initialization speed is low and the execution efficiency of CPU (Central Processing Unit) initialization is greatly reduced due to a reason that the execution time is long during the execution of typical byte filling methods in relevant technologies are solved; under the situation that the number of the bytes to be filled is greater than the preset byte number, a plurality of bytes are filled at one time, the speed of internal memory initialization is accelerated and the execution efficiency of CPU initialization is also improved.