The invention discloses an application of a mycobacterium tuberculosis PKA protein and its fusion protein in auxiliary diagnosis of pulmonary tuberculosis. The invention provides the mycobacterium tuberculosis PKA and the fusion protein through fusion expression with ESAT6. The experiment proves that the obtained PKA protein and the fusion protein can activate the body host cells to generate mycobacterium tuberculosis antigenic specificity IFN-gamma, which can be used as the candidate antigen for auxiliary diagnosis of pulmonary tuberculosis, and the mycobacterium tuberculosis PKA protein provides the new thinking for increasing sensitivity and specificity of pulmonary tuberculosis diagnosis as well as developing the novel diagnostic kit.