Femtosecond pulse filamentation has wide applications in many fields. Extending the lengths of filamentation and accompanied plasma channel are the key to application. By solving the extended nonlinear Schr dinger equation coupled with the electron density equation, we can get the following conclusion that the performance of femtosecond filamentation and plasma channels in Kerr media can be significantly improved if an superposed Gaussian beam with the same energy is used instead of an ordinary single Gaussian beam as the incident beam. According to theoretical calculation of the upper threshold power for self-focusing, the self-focusing upper threshold power of superposition Gaussian beam is larger than that of single Gaussian beam. Hence, superposed Gaussian beam as incident beam is particularly useful to extend the filament length and avoid multi-filamentation when the incident pulse energy is high.