We observed the supercontinuum in Ar during the propagation of a femtosecond pulse with wavelength of 800nm，repetition rate of 10Hz and pulse duration of 30fs. We studied the supercontinuum when changing the chirp of the pulse，pulse energy，pressure in the cell and the focal length to find the optimal conditions. And we observed the steady broadest supercontinuum extending up to 200nm with the pulse of 20mJ energe，29×104fs2 chirps when the focal length was 500mm and the pressure of the cell was 23×105Pa. We measured the far-field pattern of the continuum and found the divergence angle of the white light to be 31mrad.