Based on self-recurrence method and Fresnel-Kirchhoff diffraction formula, we have studied eigen modes and their beam quality factor M2 in the large-aperture high-power thin disk laser with gain distribution, aperture stop and tilt mirror, etc. By using eigenvector method. The large-aperture thin disk kilowatt laser system and fiber-scan measurement device is developed. The output characteristics of large-aperture thin disk laser have been studied both experimentally and theoretically. The results show that large-aperture high-power plano-concave resonator contains many eigen modes, has high misalignment tolerance, can obtain high-power laser output; the output power is quadratic function of the mirror tilt angle; the misalignment tolerance decreases as the aperture stop diameter decreases. The misalignment may bring forth new mode competition. M2 decreases as the tilt angle increases. The results obtained will be useful for the design of the high-power laser system.