  Supernova remnants (SNRs) are the most attractive candidates for the
acceleration sites of Galactic cosmic rays. We report the detection of GeV
$\gamma$-ray emission with the Pass 8 events recorded by Fermi Large Area
Telescope (Fermi-LAT) in the vicinity of the shell type SNR CTB 37B that is
likely associated with the TeV $\gamma-$ray source HESS J1713-381. The photon
spectrum of CTB 37B is consistent with a power-law with an index of
$1.89\pm0.08$ in the energy range of $0.5-500$ GeV, and the measured flux
connects smoothly with that of HESS J1713-381 at a few hundred GeV. No
significant spatial extension and time variation are detected. The
multi-wavelength data can be well fitted with either a leptonic model or a
hadronic one. However, parameters of both models suggest more efficient
particle acceleration than typical SNRs. Meanwhile, the X-ray and $\gamma$-ray
spectral properties of CTB 37B show that it is an interesting source bridging
young SNRs dominated by non-thermal emission and old SNRs interacting with
molecular clouds.
