Daylighting design in architecture has become more and more important in acting as the principal source of lighting in buildings. There are two obvious advantages of using daylight in buildings, that is, comfort of human beings and saving energy. This study attempts to investigate the daylighting performance of a newly established eco-friendly Sainsbury’s supermarket which has known to be the first supermarket in the UK fitted with the daylight sun pipes. A software package ECOTECT/RADIANCE is used as the numerical tool to carry out his research. Daylight factors and daylight illuminances at different positions in the supermarket including the goods shelves are calculated and evaluated. Three different cases with different conditions, such as, different distributions of the sun pipes and different sizes of the sun pipes, are conducted as well to compare with current design which leads to optimization.