In this paper, by preparing a molten mixture of KNO3 and Er(NO3)3, mixing it with a thin film lithium niobate in a high-temperature tube furnace for low temperature thermal diffusion, and combining it with an annealing process, a method was invented to directly dope the thin film lithium niobate with Er3+. By continuously changing parameters such as thermal diffusion temperature, doping reagent concentration ratio and crystal tangential direction, the influence of different parameters on the effect of doping Er3+ by the low temperature ion exchange method was explored through comparative experiments. When the thermal diffusion and annealing temperature were 360 ℃, and under the parameter setting of KNO3 and Er(NO3)3 mass ratio of 25∶1, a Z-cut erbium-doped thin film lithium niobate with good surface morphology was obtained. The Er3+ concentration in the obtained erbium-doped thin film lithium niobate was detected by time-of-flight secondary ion mass spectrometry, which verified the actual effect of the low temperature ion exchange method used. This method greatly simplifies the thin film lithium niobate doping process, while saving costs, and will help to achieve subsequent selectively doping on the thin film lithium niobate platform and provides a viable solution for the construction of a customized lithium niobate photonic integration platform in the future.