A memory and a method applied in one program command for the memory are provided. The memory includes a buffer and at least one program unit. The method includes the following steps. First, enter the program command to the memory. Next, enter user data to the buffer. Read the data of the program unit. Determine whether the user data fill the buffer. Fill the part of the buffer unoccupied by the user data with the data of the program unit if the user data do not fill the buffer. Erase the program unit if the program unit is not empty. Finally, program the data of the buffer into the program unit.