A cluster model consisting of 41 atoms is presented for simulating the bulk crystal and some quasi atoms are added in order to saturate dangling bonds in the cluster boundary. The SCCC-EHMO method is used to calculate the deep impurity states of neutral transition metal atoms Cr, Mn, Fe, Co and Ni in gallium arsenide. It is found that the calculated positions of the deep impurity levels in the gap are in good agreement with the experimental results.