The invention relates to a layered optimization method for a multistage multi-spraying-pipe ejector. The method comprises the following steps: (1) optimizing overall parameters of an ejector: calculating a total pressure ratio; confirming ejection stage quantity and single-stage pressure ratio; assuming a series of ejection area ratio alpha and ejection mach number M'; calculating ejection performance and optimally confirming the ejection parameters; (2) optimizing the ejection nozzle layout: designing the nozzle layout in different nozzle amount and distribution forms, performing numerical simulation and optimally confirming nozzle layout parameters; (3) optimizing the parameters of enhanced mixing ejection spraying pipes: designing the ejection spraying pipes with different tooth amount and invading angles, performing numerical simulation and optimally confirming the nozzle shape parameter. The method disclosed by the invention overcomes the defect of the present ejector design method that the shape and structure layout of the ejection spraying pipes are not considered, can obviously reduce the deviation of the theoretical design and the engineering commissioning, can reduce the technical risk and can save the development and running cost of the ejector system.