The dependence of optical signal-noise ratio on the number of optical nodes, both noise figure and gain of EDFAs is derived. The relation between the number of optical nodes and specifications of EDFAs is analyzed. Followings are concluded: 1) The number of optical nodes is about 19 under the case where the first EDFAs of optical nodes are used for the loss of nodes and the second EDFAs for the loss of fiber, and where the OSNR is required more than 20 dB; 2) To modify EDFAs′noise figure increases the number a litter; 3) It can increase the size of the all optical network up to 56 by reducing the loss of the nodes and optimizing each gain of EDFAs as well.