We proposed a strategy to synergistically enhance uranium capture capacity through photothermal desalination, and prepared a COF hydrogel (KTG) through a simple process for the first time. KTG with ideal broadband light absorption capacity could be used as an outstanding photothermal conversion material. Meanwhile, the built-in elastic honeycomb structure endowed the KTG with good mechanical properties and adequate water transport performance that accelerated the diffusion and mass transfer ability of uranyl. Under a simulated sunlight, the adsorption capacity, selectivity, adsorption rate and cycle capacity of uranium could be significantly improved. Moreover, benefiting from the outstanding photocatalytic performance, KTG exhibited a high anti-fouling activity against marine biological entities, thereby achieving long-term efficient uranium adsorption and solar desalination. Display omitted •The first example of COF hydrogel for solar desalination and uranium recovery.•COF hydrogel for synergistically enhance uranium capture through photothermal desalination.•COF hydrogel shows a high evaporation rate and exceptional uranium recovery capacity.•COF hydrogel has high anti-biofouling activity and good reusability. Capturing of uranium from the natural seawater is considered to be one of the most promising methods to meet the current demand for nuclear energy. Herein, we prepared a reduced graphene oxide-based (rGO-based) covalent organic framework hydrogel (KTG) with three-dimensional porous structure as a platform for enhancing uranium capture capacity through photothermal desalination. Under light irradiation, the KTG produces a local heat that can be used to generate steam while promoting the rapid diffusion of uranium inside the hydrogel 3D network, thereby increasing the adsorption efficiency and capacity of uranium. KTG can achieve exceptional uranium capture capacity (521.6 mg g−1) under one sun irradiation, which is 42.4% higher than that under dark conditions. In addition, excellent photocatalytic activity and mechanical properties make KTG possess high anti-biofouling activity, good reusability, and achieving continuous uranium capture and solar distillation.