The invention relates to a coal mill trip control method under a low-load three-coal mill running mode. The method comprises the steps that whether coal mill trip happens or not is determined under the low-load three-coal mill running mode; and if coal mill trip happens, judgment is made according to the actual output of a unit and the maximum output of remaining two coal mills, different controlstrategies are taken for unit fuel control, water supply control and steam turbine control, and safe and stable operation of the unit is maintained. Compared with the prior art, the problem of controlover the coal mill trip under the low-load three-coal mill running mode is solved.