A phase change memory (PCM), a writing method thereof and a reading method thereof are provided. The PCM has a plurality of memory cells. The writing method comprises the following steps. At least one stress pulse is applied for aging at least one of the memory cells. A starting pulse is applied to all of the memory cells of the PCM for decreasing a resistance of each memory cell. A detection pulse is applied to all of the memory cells of the PCM for detecting the resistance of each memory cell. A set pulse is applied to the aged memory cells. A reset pulse is applied to the non-aged memory cells.