The total reaction cross section of 17B on C target has been measured by using the transmission method at the Radioactive Ion Beam Line in Lanzhou (RIBLL). Assuming 17B consisting of a core 15B plus two halo neutrons, the total cross section of 17B 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 17B. Based on the analysis, the two neutrons halo of 17B was confirmed.