Abstract: The efficiencies are analyzed and compared to GPS data process using GA with two coding methods.GA with binary coding is prone to carry out GA operators,but its length is longer,EMS memory is larger and stability is weaker than ones of real coding.To integer nature of double-differenced ambiguity,real code were modified to round in coding then made up of individual.The results of the practical data processing show that GA with the modified real coding can be higher in reliability and get success rate on GPS ambiguity resolution than one with binary coding.