Abstract: The collector efficiency of flat plate solar collector was affected by the size of the collector in addition to the internal structural parameters,operating parameters and other factors.3-D physical models of large-scale flat plate solar collectors and parallel conventional flat plate collectors under the same heat-collecting area were established.Moreover,the relationship between the collector efficiency,heat collecting capacity and the heat losses with the change of scale of the two types of collector systems was studied and analyzed.It was found that under the same heat collecting area condition,the collector efficiency of the large-scale flat plate solar collector was increased about 4% compared with the parallel conventional flat plate collector.However,for the conventional flat plate collectors in parallel,the proportion of heat losses was increased and the collector efficiency was decreased to a certain extent with the increase of heat collecting area.On the other hand,the large-scale flat plate collectors the heat loss was decreased and the collector efficiency was increased with the increase of heat collecting area.The research conclusions could provide guidance on the size design of large-scale flat plate collectors.