Due to energy saving and flexible installation, the daylighting system via optical fibers for indoor illumination has attracted a lot of research attention. However, in applications, it is hard to adopt large aperture lens to improve sunlight collection due to the overheating problem caused by high sunlight concentration. The optical fibers generally adopted, Polymethylmethacrylate (PMMA) fiber, often suffers from overheating, and cannot work under a temperature exceeding 70 degrees C (Ashby, 2005). To solve this problem, this study tested three measures, infrared light filter (Sedki and Maaroufi, 2017), flux homogenization and fiber facet polishing, respectively to control thermal load caused by a large lens with a diameter of 1 m. The experimental data shows that the infrared light filter can reflect infrared light (740-1100 rim) efficiently, meanwhile keeping highly transparent for the visible spectrum (400-700 nm), which produces the cold incident light. A homogenizer was also designed to produce a uniform flux distribution by reflection in a mirror cavity. Analysis based on Monte Carlo rays-tracing method (MCRT) showed that the homogenizer could supply a flat flux distribution of 1500 suns by eliminating the flux peak. Microscopy experiments revealed that fine polish could effectively remove dust off the surface of the PMMA fiber, so to avoid heat spot to protect PMMA fiber. A long time daylighting test on Beijing (40 degrees 05'23 '' N, 116 degrees 17'45 '' E, 97 klux outdoor) demonstrated the feasibility of the large lens with an aperture of 1 m for daylighting via optical fibers, which offered an illumination level of 180lx on an area of 36 m(2). A comparison test on Lhasa, Tibet (29 degrees 39'52 '' N, 91 degrees 06'26 '' E) has also carried out under a higher outdoor illuminance of 125 klux, which showed a daylighting efficiency of 15.1%. The research showed that, as long as there was good thermal load control, PMMA optical fibers can work well and it is feasible to adopt large lens into daylighting system via plastic optical fibers.