This study presents an integrated opto-mechanical analysis of a PMMA Fresnel lens used in solar concentrators for concentrated photovoltaic systems. The temperature dependence of refractive index of the PMMA lens was analyzed based on its temperature coefficient of refractive index dn/dT. In addition, the thermal distortion of the Fresnel lens under various temperature rises was computed by finite element analysis (FEA). Then, the temperature induced effects, variation of refractive index and the deformed lens geometry, were imported into ray tracing simulation simultaneously. Finally, the thermal-optical effects on the optical performance of a flat Fresnel lens were successfully investigated and discussed, including the maximum irradiances on the receiver and the optical efficiencies under different temperature rises.