The invention discloses a primary frequency modulation control method of thermal generator set in CTF operation mode and a system thereof. The method comprises: a power deviation signal is multiplied by a proportional gain K to carry out range per-unit operation and the power deviation signal and a pressure deviation signal are guaranteed to be at the same range; and weighting and adding are carried out on the pressure deviation signal and the power deviation signal and then the processed signals are sent to a turbine main control unit for adjustment, wherein the weights of the pressure deviation signal and the power deviation signal are obtained by calculation based on weight functions F1(X) and F2(X). According to the invention, the method and system have the following beneficial effects: on the basis of setting of two weight functions, a power anti-regulation phenomenon caused by main stream pressure adjustment can be prevented; and the power compensation amount of the primary frequency modulation can meet the requirement of the power grid dispatching.