The ferromagnetism of carbon nanotube with vacancy defects is investigated with the Hubbard model.For small hopping integral（t2） around the defects

the ferrimagnetic ground state with spin S=1/2 per defect is obtained and the ferrimagnetism is mainly contributed by the spin at the carbon atoms around the defects and the two ends of the tube.As t2 increases to a critical value t2c

which depends on the on-site Coulomb repulsion U

the ferrimagnetic ground state is unstable.The calculation of spin density shows that t2 suppresses the spin correlation and destabilizes the ferrimagnetic ground state.