In this article, multi-reflection of radiation on both parabolic reflectors of CPC with one sided flat absorber and its effect on calculations of energy collection are theoretically investigated. Results show that, when a beam of radiation strikes on the aperture at incidence angle near zero, a considerable fraction of radiation will arrive on the absorber after more than two reflections, but the fraction of radiation that arrive the absorber after more than three reflections is considerably small. Comparative analysis of annual radiation collected by east-west oriented CPC based different reflection models indicates that the two-reflection model where more than three reflections are not considered can accurately estimate the annual collectible radiation, and for the case of CPCs with high reflectivity such as larger than 0.8 and larger acceptance angle such as larger than 20 degrees, the one-refection model where more than two reflections are not considered is acceptable to estimate annual radiation collected by CPC. (C) 2013 Elsevier Ltd. All rights reserved.