The total reaction cross section of B-17 on C target has been measured by using the transmission method at the Radioactive Ion Beam Line in Lanzhou (RIBLL). Assuming B-17 consisting of a core B-15 plus two halo neutrons, the total cross section of B-17 on C target was calculated with the zero-range Glauber model where Gaussian plus HO density distributions were used. It fitted the experimental data very well. A large diffusion was found about the density distribution of B-17. Based on the analysis, the two neutrons halo of B-17 was confirmed.