Distance measurement of gamma-ray pulsars is a current challenge in pulsar studies.The Large Area Telescope（LAT） aboard the Fermi gamma-ray observatory discovered more than 70 gamma-ray pulsars including 24 new gamma-selected pulsars with almost no distance information.We study the relation between gammaray emission efficiency（η=Lγ/E˙） and pulsar parameters for young radio-selected gamma-ray pulsars with known distance information in the first gamma-ray pulsar catalog reported by Fermi/LAT.We have introduced three generation-order parameters to describe the gamma-ray emission properties of pulsars,and find a strong correlation of η-ζ3,a generation-order parameter which reflectsγ-ray photon generation in the pair cascade processes induced by magnetic field absorption in a pulsar＇s magnetosphere. A good correlation of η-BLC,the magnetic field at the light cylinder radius,is also found.These correlations are the distance indicators in gamma-ray pulsars used to evaluate distances for gamma-selected pulsars.Distances of 25 gamma-selected pulsars are estimated,which could be tested by other distance measurement methods.The physical origin of the correlations may also be interesting for pulsar studies.
