It is still an urgent task to find new two-dimensional (2D) semiconductor materials with a suitable band gap, high stability and high mobility for the applications of next generation electronic devices. Based on first-principles calculations, we report a new class of 2D group-11-chalcogenide trielement monolayers (MNX, where M = Cu, Ag, Au; N = Cu, Ag, Au; X = S, Se, Te; M ≠ N) with a wide band gap, excellent stability (dynamic stability, thermodynamic stability and environmental stability) and high mobility. At the mixed density functional level, the energy band gap extends from 0.61 eV to 2.65 eV, covering the ultraviolet-A and visible light regions, which is critical for a broadband optical response. For δ-MNX monolayers, the carrier mobility is as high as 104 cm2 V-1 s-1 at room temperature. In particular, the mobility of δ-AgAuS is as high as 6.94 × 104 cm2 V-1 s-1, which is of great research significance for the application of electronic devices in the future. Based on the above advantages, group-11 chalcogenide MNX monomolecular films have broad prospects in the field of nanoelectronics and optoelectronics in the future.