The invention discloses a modeling method of ultrahigh voltage AC-DC power transmission in power supply optimal planning. The method comprises the following steps that system basic information is acquired; a production simulation model is determined according to the system basic information, wherein there are three types of production simulation models including a three-stage output module, a specified curve model and a conventional unit model; and the output parameter of power transmission is corrected according to the determined production simulation model based on the transmission end unit parameter and the receiving end power grid electricity utilization parameter under the production simulation model so that an optimized model corresponding to ultrahigh voltage AC-DC power transmission is acquired. According to the modeling method, the output characteristic and the adjusting characteristic of ultrahigh voltage AC-DC power transmission can be fully considered, and the influence of ultrahigh voltage AC-DC power transmission on receiving end power grid power supply operation can be more accurately reflected in power supply optimal planning so that the rationality of power grid planning can be enhanced and thus the economic benefit can be enhanced and waste of electricity can be reduced.