The Vela pulsar represents a distinct group of \gamma -ray pulsars . Fermi \gamma -ray observations reveal that it has two sharp peaks ( P1 and P2 ) in the light curve with a phase separation of 0.42 and a third peak ( P3 ) in the bridge .
The location and intensity of P3 are energy-dependent .
We use the 3D magnetospheric model for the annular gap and core gap to simulate the \gamma -ray light curves , phase-averaged and phase-resolved spectra .
We found that the acceleration electric field along a field line in the annular gap region decreases with heights .
The emission at high energy GeV band is originated from the curvature radiation of accelerated primary particles , while the synchrotron radiation from secondary particles have some contributions to low energy \gamma -ray band ( 0.1 - 0.3 GeV ) .
The \gamma -ray light curve peaks P1 and P2 are generated in the annular gap region near the altitude of null charge surface , whereas P3 and the bridge emission is generated in the core gap region .
The intensity and location of P3 at different energy bands depend on the emission altitudes .
The radio emission from the Vela pulsar should be generated in a high-altitude narrow regions of the annular gap , which leads to a radio phase lag of \sim 0.13 prior to the first \gamma -ray peak .