A method for purifying combustion exhaust gas, comprising: placing a denitration catalyst in gas stream to remove nitrogen oxides from a combustion exhaust gas, wherein the denitration catalyst comprises a shaped product comprising a catalyst component and having microcracks on the surface of the shaped-product, and 80% to 100% of the microcracks on the number basis have an angle of a longitudinal direction of the microcracks with respect to a main direction of the gas stream within ±30 degrees.