We studied the special roles of loose neutron-halo structure of 19 B on the fragmentation and momentum dissipation by using isospin dependent quantum molecular dynamics. In order to protrude the special roles of neutron-halo structure on the reaction dynamics we compared the fragmentation multiplicity and nuclear stopping (momentum dissipations) induced by neutron-halo nucleus 19 B with those induced by a same mass stable nucleus 19 F under the same incident channel condition. We found that the loose neutron-halo structure of 19 B increases the fragmentation multiplicity in lower beam energy region. On the contrary, the special halo structure of 19 B weakens the nuclear stopping, compared to those induced by stable nucleus 19 F. However both fragmentation multiplicity-difference and nuclear stopping-difference between the reactions induced by 19 B and 19 F gradually decrease and finally disappear as the increase of beam energy. These results suggest a good project for the experimental measurements of the fragmentation multiplicity and nuclear stopping to study the reaction dynamics induced by neutron-halo nuclei.