A measurement method of the high dynamic range laser focal spot was proposed. First of all, the mathematical model of schlieren method to measure the far-field focal spot was constructed,the main lobe intensity amplification coefficient and the laser spot amplification coefficient were confirmed, and the parameters were calibrated by automatic alignment laser beam; Secondly, the schlieren ball was put in focus position of side lobe laser beam to shade the spot centre and side lobe image was captured accurately by integrated diagnostic beam fast automatic alignment system; Finally, the schlieren reconstructed algorithm was optimized by calculating side lobe image centre and image fusion, and the error of traditional schlieren reconstruction method for side lobe center was decreased and the obvious edge of reconstructed image was eliminated. The application in parameter measurement integrated diagnostic system of the high power laser facility to measure far-field laser focal spot shows that the method can measure the far field distribution of high dynamic range laser focal spot exactly if the parameter of the mathematical model is calibrated accurately and the schlieren reconstructed algorithm is optimized.