Solar thermal power is a very promising technique in the future, while the design of heliostat field, which decide the investment and the energy received, influences very much thermoeconomics of the power system so as the capital cost of the electricity obtained in the end. In this paper, the design of heliostat field with traditional tracking method is based on a radial staggered layout, which ensures no mechanical touching, is optimised with a multi-objective optimiser 8MOO9 based on two objectives (specific energy cost versus investment cost). The resulting Pareta curve coordinated with two objectives shows all the optimum solutions, which also demonstrates that with the optimisation, fields with lower specific energy costs compared to published cases can be achieved, which are well distributed as well. Furthermore, the relationship between the decision variables and the energy concentrated are discussed, which will be useful for the design of helistat field.