In this paper, the process of unpinning spiral waves from obstacles with pulses of radial electrical field (PREF) in excitable medium is studied by using Barkley model. We use a radial electrical field to simulate the field of an needle electrode placed in the middle of a round obstacle. Numerical results show that the PREF can separate spiral waves from obstacles effectively. With a single pulse of radial electrical field (SPREF), spiral waves can be unpinned from an obstacle effectively in a weakly excitable medium, but it cannot be unpinned in a strongly excitable medium. The unpinning parameter space of an SPREF is larger than that of a uniform electric field or anti-tachycardia pacing. Multiple pulses of radial electrical field (MPREF) is effective for unpinning in the entire parameter space where spiral waves exist. Compared with other methods to unpin spiral waves, the PREF method has the advantages of low electric field magnitude, high success rate, and large application range in the parameter space. And unlike other methods, the PREF has a success rate insensitive to the phase of the spiral wave on the obstacle. We hope that this method will provide a new idea for clinical treatment for related cardiac diseases.