The aim of this paper is to model the heliostat field in central receiver solar power plant (CRSPP) for a given input power. An in-house computer program is developed based on the vector geometry to select an individual heliostat and calculate its characteristic angles at any time of the day, any day of the year and any location on earth. This program is also used for open loop control of the heliostat field. To find the layout of heliostat field, the radial staggered configuration is used for the heliostat field as one of the best configurations used so far. Then, the locations of heliostats are determined and the efficiency of each heliostat is calculated in order to find the most efficient heliostats in the field. The heliostats with higher efficiency (more than 80%) are chosen to be located in the field. Then, by calculating the input power of each heliostat supplied to the receiver, the absorbed heat power by the receiver is calculated. Consequently the minimum number of heliostats with their locations is determined for a specific heat power. The results show that for a 20MWt (thermal power) CRSPP, 294 heliostats are needed which result in a heliostat layout with 86.45% total efficiency.