Two-dimensional (2D) magnetic crystals have attracted great attention due to their emerging new physical phenomena.They provide ideal platforms to study the fundamental physics of magnetism in low dimensions.In this research,magnetic tunneling junctions (MTJs) based on XSe2 (X =Mn,V) with room-temperature ferromagnetism were studied using first-principles calculations.A large tunneling magnetoresistance (TMR) of 725.07％ was obtained in the MTJs based on monolayer MnSe2.Several schemes were proposed to improve the TMR of these devices.Moreover,the results of our non-equilibrium transport calculations showed that the large TMR was maintained in these devices under a finite bias.The transmission spectrum was analyzed according to the orbital components and the electronic structure of the monolayer XSe2 (X =Mn,V).The results in this paper demonstrated that the MTJs based on a 2D ferromagnet with room-temperature ferromagnetism exhibited reliable performance.Therefore,such devices show the possibility for potential applications in spintronics.