A data accessing method for a memory storage apparatus is provided. The method includes using a first check code circuit to generate a first check code corresponding to a first data stream and generating a first data set based on the first data stream and the first check code. The method also includes using a second check code circuit to obtain the first data stream and the first check code from the first data set and check the first data stream according to the first check code. The method still includes using a third check code circuit to generate a second check code according to the checked first data stream and generating a data frame based on the checked first data stream and the second check code and thereby programming the data frame into a physical programming unit.