  The AMS-02 collaboration has just released its first result of the cosmic
positron fraction $e^+/(e^-+e^+)$ with high precision up to $\sim 350$ GeV. The
AMS-02 result shows the same trend with the previous PAMELA result, which
requires extra electron/positron sources on top of the conventional cosmic ray
background, either from astrophysical sources or from dark matter
annihilation/decay. In this paper we try to figure out the nature of the extra
sources by fitting to the AMS-02 $e^+/(e^-+e^+)$ data, as well as the electron
and proton spectra by PAMELA and the $(e^-+e^+)$ spectrum by Fermi and HESS. We
adopt the GALPROP package to calculate the propagation of the Galactic cosmic
rays and the Markov Chain Monte Carlo sampler to do the fit. We find that the
AMS-02 data have implied essential difference from the PAMELA data. There is
{\rm tension} between the AMS-02 $e^+/(e^-+e^+)$ data and the Fermi/HESS
$(e^-+e^+)$ spectrum, that the AMS-02 data requires less contribution from the
extra sources than Fermi/HESS. Then we redo the fit without including the
Fermi/HESS data. In this case both the pulsars and dark matter
annihilation/decay can explain the AMS-02 data. The pulsar scenario has a soft
inject spectrum with the power-law index $\sim 2$, while the dark matter
scenario needs $\tau^+\tau^-$ final state with mass $\sim 600$ GeV and a boost
factor $\sim 200$.
