In general， there are variable and fixed setting modes for frequency bias coefficients in automatic generation control（AGC）. Based on theoretical analysis and model simulation， it is proposed that the influence on frequency and tie-line power interchange be small when using variable or fixed coefficients under the existing system technical conditions. And as long as the total frequency bias coefficient is fixed， under the condition of sufficient reserve capacity and available transfer capability， it does not affect the system frequency quality by distributing frequency bias coefficients in different proportions. Finally， according to the existing system technical conditions and future developmental tendency， rational proposals for setting frequency bias coefficients are put forward on the principle of fair distribution of the area secondary frequency regulation obligation.