Time delay estimation (TDE) is of great importance in a TDOA based location finding system and cross correlation is a typical method of TDE. This paper presents a new index named Equivalent One-bit Adding Times (EOAT) to evaluate algorithm’s computation on bit level, based on which a low-complexity method of correlation is presented, meanwhile, we deduce the sufficient condition under which new method could be used, where condition coefficient F is put forward whose value is decided by input signal’s nature, sampling rate and ADC’s bits.