The transmission properties of femtosecond optical pulse are analyzed with the momentum method. The results show that the third order dispersion and self steep directly affect not only the property of symmetry of pulse, but also the width of it. The results are independent of the shape of pulse, and so it is of certain universalism. Using the pulse in the shape of sech 2, the approximate solution has been obtained and compared with the numerical simulation of evolution equation. This work will be helpful to the theory and experiment of 10 fs～100 fs optical pulse transmission within short distance.