Abstract: The present disclosure relates to a method and system for determining a technical limit well spacing for chemical flooding for a heavy-oil reservoir. This method includes: establishing a reservoir numerical simulation model; setting up injection and production wells according to a set well spacing, and using the reservoir numerical simulation model to calculate an average pressure, an average crude oil viscosity and an average permeability at each grid point between the injection and production wells within m days; calculating a driving pressure gradient of each grid point, and drawing a driving pressure gradient curve; calculating a starting pressure gradient of each grid, and drawing a starting pressure gradient curve; determining a relationship between the driving pressure gradient curve and the starting pressure gradient curve. In this manner the present disclosure calculates the limit well spacing for chemical flooding for the heavy-oil reservoir after steam stimulation.