The technique of the focus plane array (FPA) or the multi-beam feed system has been more and more widely applied in radio astronomy. Much more information of electric and magnetic field collected at the focus plane could be used to fasten the observational procedure several or even several tens times by scanning the telescope over the extended sources. The image quality observed can be improved by subtracting or removing effects of fluctuation or irregularity in the atmosphere or the ionosphere, and by monitoring or controlling the accuracy of the main reflector, the subreflector and the pointing of the telescope. Costs and requirements for the accuracy of huge radio telescopes or space radio telescopes might be much reduced by introducing the FPA in monitoring and adjusting telescopes in the future. The FPAs have been equipped widely on millimeter and sub-millimeter radio telescopes and main bands of large radio telescopes in the world. The paper will review the situation of that by listing operating feeds for the latter and describing briefly the FPAs equipped on the former. The restriction of applying the FPAs on telescopes and corresponding phase errors will be briefly analyzed in this paper. Consideration of the cost and prospect of application of the FPA are also shortly given. Finally tentative valuation and suggestion of applying the FPA on the FAST, a planned huge spherical radio telescope with active main reflector, are followed. Arrangement of frequencies, beams, LNAs and corresponding system temperature suggested by experts from China and Jodrell Bank Radio Observatory is listed at last.