Disclosed is a method for detecting a block with an instable electrical property in a flash memory, the method relating to a control chip (1), a software program module (2) and a flash memory chip (3), wherein the control chip (1) is in signal connection with the software program module (2) and the flash memory chip (3) respectively. The method comprises: firstly writing test data into the first page of all blocks; then erasing all the blocks; writing the test data into all the pages of all the blocks; and finally comparing the data in all the pages of all the blocks and obtaining a bad block table according to a result. The method has a simple principle, realizes high work efficiency and can find a bad block with data written into the block being error-prone due to the fact that erasure is performed when the number of pages written does not exceed six.