The invention relates to a water injection experimental device and method for automatic crude oil sampling systems, belonging to the technical field of pipeline system. The water injection experimental device is a sled as a whole; a water inlet of the water injection experimental device is connected with a water pipe, and a water outlet of the water injection experimental device is connected witha water injection hole of a crude oil main pipe. The water injection experimental device, on a connecting pipeline from the water inlet to the water outlet, is provided with a first manual shut-off valve, a first pressure gauge, a filter, a second pressure gauge, a water injection pump, a third pressure gauge, a flow meter, a check valve, and a second manual shut-off valve in sequence. The connecting pipeline is connected with a regulating pipeline between the outlet of the water injection pump and the third pressure gauge to regulate the flow rate of the pressurized water. The device can meetthe requirements of water injection tests of all the automatic crude oil sampling systems in the same project, match different water injection volume ranges, eliminate the influence of the return flow of the crude oil medium caused by the failure of a connecting valve, and improve the safety and reliability of the pipeline operation.