The invention provides a method for determining injection pressure at a natural gas pool-forming period of a dense reservoir. The method comprises the steps of clearly studying natural gas reservoir forming source rock of the dense reservoir and the reservoir, and regulating that the natural gas migration direction in dense reservoir natural gas reservoir forming is a source rock pointing reservoir; in the natural gas migration direction in the dense reservoir natural gas reservoir forming, determining adjacent air layers and dry layers or air layers and water layers through a natural gas reservoir forming section; obtaining mercury injection threshold pressure of the adjacent air layers and dry layers or air layers and water layers, and obtaining pressure average values thereof; and performing conversion on the dense reservoir natural gas reservoir forming capillary pressure and mercury injection threshold pressure, namely determining injection pressure at the natural gas pool-forming period of the dense reservoir. The method for determining injection pressure at the natural gas pool-forming period of the dense reservoir has data reliability and accuracy.