In order to ensure the performance and economic benefits of oil sands developed by steam-assisted gravity drainage（SAGD），well spacing evaluation is performed for Block A in Longlake Oilfield，Canada. Firstly，according to the distribution of geological parameters of the area，the cumulative oil production is used as the evaluation index to screen the main geological controlling factors. Secondly，numerical simulation is used to clarify the influence of single main geological controlling factor on development indicators. Finally，considering the well drilling and completion investment，crude oil price，and other economic parameters，the net present value is used as the indicator to evaluate the economic benefits of various well spacing under the complex geological factors. An optimal screening method and the process to optimize SAGD well spacing are obtained by comprehensively considering geological conditions，development effects，and economic benefits.The preferred method and process achieve a rapid optimization of reasonable well spacing at a target oil price. For Block A in Longlake Oilfield，oil layer thickness，interbed distribution，high water saturation interlayer thickness，and top water layer thickness are four main geological controlling factors. According to the geological parameters of Block A，the average thickness of the preferred oil layer is 25 m，the interbed distribution is 60%，the high water saturation interlayer thickness is 3.7 m，and the top water layer thickness is 2.2 m. When the oil price is 50 US dollars per barrel，the recommended well spacing is 102 m，which is close to the well spacing（100 m）calculated by the actual model corresponding to the maximum net present value.