The invention discloses a load regulation speed dynamic regulating method and device under the AGC mode of a thermal power generating unit. The load regulation speed dynamic regulating device comprises a subtracter module DEV1, an absolute value module ABS and a function setting module F(x) which are sequentially connected in series, wherein the subtracter module DEV1 is connected with a high/low amplitude judgment module HLALM in series; the output ends of an analog quantity generator A1, the function setting module F(x) and the high/low amplitude judgment module HLALM are respectively connected with the input end of a selector module AXSEL. The load regulation speed dynamic regulating method and device under the AGC mode of the thermal power generating unit has the advantages that, through dynamically regulating the regulation speed, it can ensure that the load regulation of the unit can be quickly performed when the main steam pressure is stable, so as to quickly reach the load target value required by scheduling and achieve the optimization of the examination index.