The optical efficiency of the heliostat field is one of the most crucial factors in solar power tower (SPT) technology. The design of heliostat field always costs much computing time to get one accurate result of the blocking and shading factor, which influences the optical efficiency of the heliostat field significantly. A predicting model was developed, which took advantage of flat mapping method to avoid unnecessary calculations. An improved code combining the flat mapping and ray tracing methods was presented, which was superior to the known codes no matter in computing accuracy or computing speed. With the computing code developed, an optimizing code making use of both the Rosen projection method and simulated annealing smart algorithm was created to optimize each parameter of the heliostat field. Comparisons between the radial staggered and the biomimetic spiral layouts of heliostat field were executed for the built commercial plants by the new developed code. The analysis found that the spiral layout was more competitive in the north field, while it behaved worse in the circular and south field because of cosine effect. A hybrid field combining two types of layouts was proposed, which behaved better than both spiral and staggered layouts. (C) 2015 Elsevier Ltd. All rights reserved.