Distance measurements of gamma-ray pulsars are challenging questions in present 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 which nearly have no distance information. We study the relation between gamma-ray emission efficiency ($��=L_��/\dot E$) 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 gamma-ray emission properties of pulsars, and find the strong correlation of $��-��_3$ a generation order parameter which reflects $��$-ray photon generations in pair cascade processes induced by magnetic field absorption in pulsar magnetosphere. A good correlation of $��-B_{\rm LC}$ the magnetic field at the light cylinder radius is also found. These correlations would be the distance indicators in gamma-ray pulsars to evaluate distances for gamma-selected pulsars. Distances of 25 gamma-selected pulsars are estimated, which could be tested by other distance measurement methods. Physical origin of the correlations may be also interesting for pulsar studies.

accept for the publication in RAA, 8 pages, comments are welcome