Based on the Kirchhoff approximation for the rough surfaces with small slopes, the electromagnetic scattering from the one dimensional fractal sea surface with the actual spectrum of the sea is studied by the pulse beam wave incidence. The distributions of the two frequency scattering cross section with different fractal dimension, incident angle and the center frequency are analyzed with millimeter wave incidence. The numerical result shows that there exists the largest coherence bandwidth for the two frequency scattering cross section at the specular direction. The coherence bandwidth will increase with decreasing the fractal dimension and with increasing the incident angle and the center freqquency. It also shows the scattering power which is a pulse shape but with a pulse broadening for the incident power being δ function, this pulse broadening is inversely proportional to the coherence bandwidth.