Based on finite volume method, the steady-state thermal performances of the flat-plate solar collector are studied by taking account of absorber plate thickness, collector tube spacing, collector tube length, collector tube diameter and insulating layer thickness. A physical model of gilled fiat-plate solar collector is built, then the numerical simulation of the model is carried out and the numerical simulation results are compared and analyzed with experimental results. The results show that: Either increasing the absorber plate thickness or reducing the collector tube spacing can significantly improve the instantaneous efficiency of the collector. Setting the solar radiation intensity of 700 W/m(2) and the environmental speed of 4 m/s, when the absorber plate thickness increases from 0.1 mm to 2.1 mm, the collector instantaneous efficiency increases from 46.57% to 64.03%. When the collector tube spacing decreases from 170 mm to 50 mm, the collector instantaneous efficiency increases from 52.81% to 66.01%. Reducing the collector tube length and increasing collector tube diameter are both conducive to improve the instantaneous efficiency of the collector. When the collector tube length decreases from 2800 nun to 1200 mm, the collector instantaneous efficiency increases from 57.50% to 60.12%. When the collector tube diameters increases from 8 mm to 20 mm, the collector instantaneous efficiency increases from 56.18% to 63.97%. When the thickness of insulating layer is 30 mm or more, increasing its thickness has no significant effect on improving the instantaneous efficiency of the collector. The research results are helpful to optimize the design parameters of the fiat-plate solar collector. (C) 2015 Elsevier Ltd. All rights reserved.