Through systematic analysis and calculation of the influence factors of the absolute band gap for 2D triangle lattice photonic crystal with air pore,we found the relation between complete band gap and the two main influence factors,fill ratio,background dielectric constant. The results of calculation show that the complete band gap shows up when the fill ratio f>0.4,increasing fill ratio leads to an increase of band gap width,the largest band gap can be obtained where f=0.483. Further,the larger fill ratio is,the higher the central frequency of the gap is. When f=0.483,the complete band gap shows up when the background dielectric constant ε>8. The width of band gap increases with the increase of ε.