The invention discloses a theory line loss computation method of a distribution network with a draught fan, and relates to a power distribution network theory line loss computation method. The theory line loss computation method of the distribution network with the draught fan fully considers influences of draught fan output force and tide direction on distribution network voltage, can help distribution network dispatching personnel to obtain a theory line loss computation result comparable to a true value and high in accuracy under the condition that the draught fan output force can not be measured, timely adopts highly targeted optimization measures to reduce line loss, improves economic benefits of the distribution network, and has high practical value and economic value.