小尺度自聚焦是威胁强激光装置安全运行的重要因素，需确定装置激光束发生小尺度自聚焦的临界点，以指导装置的安全运行。提出利用输出光束近场强度熵值变化来反映激光束小尺度自聚焦发展过程的方法，通过数值模拟研究了小尺度自聚焦发展过程中的近场强度熵值变化规律，利用此规律给出了强激光装置中发生显著小尺度自聚焦的近场强度熵值预警方法。通过与光束近场调制度及对比度方法的对比分析，发现该方法对小尺度自聚焦发生的表征更明显。

Small-scale self-focusing is an important factor threating the safe operation of intense laser facility, and estimating the marginal value of small-scale self-focusing in laser beam is an important part of the guidance for the safe operation of intense laser facility. The method of using near-field intensity entropy of the output laser beam to reflect the small-scale self-focusing development in laser beam is proposed. Then the variation regular pattern of near-field intensity entropy with the development of small-scale self-focusing is studied by numerical simulation. Using this regular pattern, an early-warning method is given for the obvious small-scale self-focusing happening in intense laser facility. By contrast with the methods of modulation ratio and contrast ratio, the proposed method offers a more obvious assessment.