Abstract: In this research we aim to obtain a more reliable early warning criterion for debris flow universal equipment, improve the early warning accuracy of monitoring equipment for hidden dangers of geological disasters at single point, reduce false alarm rate, and improve the capability of grassroots organization to prevent and respond to geological disasters. We propose a rainfall iterative approximation method and its steps. According to the measured rainfall values measured by monitoring equipment that have been installed in the debris flow gullies, we can gradually revise the warning criterion set last time by comparing the monitored values and analyzing whether debris flow happens,and eventually reach or approach the accurate early warning value. The first step is to collect the measured or existing rainfall data,and analyze the relationship between the initial value and the occurrence of debris flow disaster; subsequently, we can obtain the early warning value by using the proposed iterative approximation method, and finally determine the early warning criteria of different levels according to the early warning standards. We applied this method to determine the early warning criteria of different levels of rain gauges for Qiangba main gully debris flow in Wenxian County, Longnan City as an example. The research findings offer reference and guidance for the monitoring and early warning of debris flow with universal equipment in Gansu Province, and has practical significance.

Key words: debris flow, early warning criterion, rainfall, iterative approximation method, monitoring and early warning, universal equipment, early warning precision