The invention relates to a load frequency control method for a photo-thermal power generation-contained hybrid power system. A time-lag power system is divided into three regions, namely I region, IIregion and III region. The I region contains a photo-thermal power generation system, a thermal power generation system and a wind power generation system. The II region and the III region comprise athermal power generation subsystem and a wind power generation subsystem. The load frequency control method comprises the following steps of (1) establishing a mathematical model of each region; (2) establishing a state model of each region, wherein the interference caused by the uncertain terms of system parameters and the load fluctuation are taken into consideration for the state model; (3) according to the state model, designing a sliding film switching surface Si(t) with an integral; (4) according to the designed switching surface, designing a load frequency controller ui(t), adopting theui(t) as a control instruction, and controlling the load frequency of the power system. According to the invention, the communication delay of the power system is considered. The photo-thermal powergeneration system participates in frequency modulation, so that the fluctuation problem of a wind power generating set is effectively solved. The method is high in control precision and strong in robustness. The frequency deviation can be reduced.