Predicting spatiotemporal trend of the future climate in Lake Poyang Basin using CMIP5 global climate models downscaled by downscaling methods can provide data, technology, and theoretical support for the ecological and environmental protection of the basin. In current research area downscaling methods mainly include dynamic downscaling method and statistical downscaling method, among which statistical downscaling method based on linear regression is widely used thus defective in modeling non-linear relationships. In order to build up a better downscaling model, the deep learning ased spatial downscaling method (DLDM) which is more efficient in learning climate data features is established by simplifing the original network structure of U-Net, adding an interpolation layer at the head of the network, and using the deconvolution algorithm as upsampling algorithm. Then based on climate models as IPSL-CM5A-LR and BCC-CSM1.1, simulating ability of downscaled climate model is verified by making contrastive analysis to observed data from 18 meteorological stations in Lake Poyang Basin from 1965 to 2005 on fitting precision and ability to simulate extreme weather events. The results show that DLDM has higher fitting accuracy over the linear regression based statistical downscaling method and IPSL-CM5A-LR has higher fitting accuracy over BCC-CSM1.1. Based on high spatial resolution data of IPSL-CM5A-LR downscaled by DLDM from 2006 to 2100, the spatiotemporal trend of future climate in Lake Poyang Basin under RCP2.6 and RCP8.5 emissions scenarios is studied through M-K analysis and wavelet transform. The results show that the future temperature of the basin will continue to increase under the two scenarios, showing four high temperature centers located in the central north, west, east, and south of the basin. Under the RCP8.5 scenario, the temperature of the basin will be higher, and the warming trend and local cycle change will be more obvious. The future precipitation in the basin will increase first and then decrease under the two scenarios, and the changing trend is relatively gentle, showing three precipitation centers in the north, the central east, and the south of the basin. In the future, there will be "drought-wet" alternation for five times. Under the RCP8.5 scenario, the precipitation in the basin will be less and the change will be more intense, and there will be a sudden change and periodic oscillation at around 2075.