The synthesis method of high molecular weight glycidyl azide polymer (HL-GAP) is described. The experimental results indicate that the azidation of the precursor,polyepichlorohydrin (PECH),is always accompanied with its chain-breaking. In order to prepare high molecular weight and high azidized product,the influence of catalyst,antioxydant,inert gas protection and other factors on the HL-GAP molecular weight (M_w) and its distribution were experimentally investigated. After optimization of the above said factors,the M_w of HL-GAP was increased to 1.5×10⁵ and 2.95×10⁵ with azidation rate (R_a) of 99.16% and 69.20%,respectively,much higher than Vandenberg′s report in USP 3 645 917 (M_w=5×10⁴，R_a=49%).