  GRB 140903A, a short duration $\gamma-$ray burst (SGRB) detected by {\it
Swift}, is characterized by its long-lasting radio emission among SGRBs. In
addition to the $\sim 10^{6}$ s radio afterglow emission, the afterglow of GRB
140903A displays a plateau from $10^3$ s to $7 \times 10^3 $ s in the X-rays.
In this work, we attribute the X-ray plateau to the energy injection into the
decelerating blast wave and then model the later radio/optical/X-ray afterglow
emission within the standard fireball afterglow model. The afterglow emission
has been well reproduced with reasonable physical parameters, including a jet
half-opening angle $\sim 0.05$. We also compare the physical properties of
SGRBs with and without radio afterglow detections and find that nearby SGRBs
are brighter and easier to be detected in radio. Such a phenomena has been
interpreted within the afterglow model.
