Brominated tert octyl phenol formaldehyde resin (PR) is an important cross linker for chlorinated butyl rubber (CIIR). There are two competitive reactions in the vulcanization process of CIIR, the cross-linking reaction and the self-poly-condensation reaction of PR. The cross-linking density was measured by the equilibrium swelling method. The results showed: with the increasing of PR content, the cross-linking density increased when it was less than 10 phr, and decreased when the PR content exceeded 10 phr. The kinetics equation of cross-linking reaction and the self-poly-condensation reaction was obtained by non-isothermal DSC method. The results showed that the concentration index n(2) of PR in the cross-linking reaction was far less than the concentration index n(3) of PR in the self-poly-condensation reaction. The self-poly-condensation reaction was more sensitive to the concentration of PR. This explained that the cross-linking density was out of proportion with the cross linker PR content. The mechanical properties and the dynamic mechanical properties were investigated by the universal testing machine and the dynamic mechanical performance analysis (DMA), respectively. The results showed that the cross-linking density had a great impact on the mechanical properties and the dynamic mechanical properties, and the variation trend of the cross-linking density was further confirmed by the corresponding variation of the properties. When the PR content was 5 phr, the CIIR vulcanizates had better mechanical properties.