The weak short gamma-ray burst (GRB) 170817A was accompanied by the GW170817 gravitational-wave event and is believed to have been produced by an off-beam relativistic jet. Here, we use the Ep,i-Eiso and GEiso relations to determine its Lorentz factor γ and the viewing angle from the edge of the jet θ ′obs of GRB 170817A. Our results indicate that Γ = 13.4-5.59.8 and θ ′obs=4°3-1.51.8, corresponding to an on-axis = Ep,i= 415-167361 ke V Eiso =(2.4-1.91.6)erg. Therefore, the GRB was an intrinsically weak short GRB. We also find that the afterglow emission was in good agreement with the follow-up multiband observations and that the radio emissions at around 20 days may have come from the off-axis jet. Interestingly, the Doppler factor and luminosity follow a universal relation for GRBs and blazars, thus suggesting that they may share a similar radiation mechanism. ©2 017. The American Astronomical Society. All rights reserved.