The temporature of the geothermal tail water cools down after heat exchange. Tail water, even after treatment of filtering and degas treatment, still contains some suspending particles and gases. Hence reinjection would inevitably cause some negative impacts on the geothermal reservoir, such as reservior blockage induced decrease of reinjection rate, reservoir temperature drawdown lead to inmature thermal breakthrough. This will largely affect the sustainability of reinjection practices at sandstone geothermal reservoir. Evaluating the influence of reinjection in sandstone geothermal reservoir is of great significance to promote largescale reinjection practices, sustainable development and protection of geothermal resource. Based on the geothermal tailwater reinjection test of the Guantao Formation geothemal reservoir, the paper established a set of evaluation indexes, in which the change rate of geothermal water chemical contents before and after the reinjection was used to evaluate the influence of reinjection to the geothermal fluid, and the temperature change rate to evaluate the influence of reinjection to the geothermal reservoir temperature, and the change rate of specific yield, permeability change ratio, and ratio of unit recharge to evaluate the severity degree of reinjection blockage, and finally set up the influence classification standard. The evaluation results show that the reinjection did not change the chemical composition of geothermal fluid. The blockage mainly occurred around reinjection wells. The specific yield fell down by 14. 3%～59. 0% after reinjection, and the permeability is about 41%～86% of its initial value, and the reinjection rate at later stage is about 51%～92% of that at the early stage, suggesting that the reinjection blockage severity is classified into medium to severe. The distance between the pumping and reinjections wells ranges from 180 to 500 m and it has less influence on the thermal reserves temperature after the rejection of one heating season. The reinjection has caused an obvious temperature drawdown at the geothermal reservoir near the reinjection well case, with the temperature recovering from 35. 7℃ to 40. 53℃ after 224 days of shutdown at nonheating season, at the temperature recovery rate of 0. 036～0. 022℃/d. It needs another 658 days to recover to its original temperature (55℃). The water level of geothermal reservoir in this area is still declining, but reinjection can delay the decline rate of reservoir water level.