Abstract: Taking into account of various factors which effect the reconstruction precision of EAS events and selecting some suitable optimum algorithn (such as simplex method algorithm, DFS algorithm). A new software EAS-FIT is made, which is of wider use and described briefly with some applications. This new software was been used to analyse the EAS raw data of Beijing Huairou array. The results show that it can improve overall precision of the array and greatly increse the speed of off line reconstruction (20-120 times faster than the old one). In addition, some important physics results can be obtained such as energy spectrum at the ‘keen’ region and so on.

Key words: cosmic pays extersive air shower(EAS), reconstruction optimum algorithm, simplex method