A simulation system for an in-situ column experiment in a groundwater well and a simulation method are provided. The simulation system includes: an experimental column device, a sample taking device, and a sample injection device, where solid remediation agent and/or aquifer sediment are provided within the experimental column device, and is configured to be capable of being arranged in an experimental well and located below a water level; a bottom of the experimental column device is provided with a water inlet, and a top of the experimental column device is provided with a water outlet, where the top water outlet connects to the sample taking device, and the bottom water inlet connects to the sample injection device.