The present invention relates to a method for computing correlation of a PN sequence and a circuit thereof. A plurality of input values of an input sequence is summed up to give a first sum. A PN sequence comprising a plurality of first values and a plurality of second values, which correspond to the plurality of input values, are received. Summing up the plurality of input values corresponding to the plurality of first input values in the PN sequence gives a second sum. According to the first sum and the second sum, a correlation value is given. The present invention uses a simple method for computing correlation of a PN sequence. Hence, the operation efficiency is enhanced and the time to give the correlation of the PN sequence is shortened.