REBa₂Cu₃O_7-x high-temperature superconducting coated conductors (CCs), i.e. the second generation high-temperature superconducting tapes, with excellent current carrying properties and mechanical behaviors, are potentially applied in the fields of power, transportation, medical care, and military, receiving extensive attention from superconductor research teams at home and abroad in recent years. Increasing the thickness of the superconducting layer in CCs is facilitated to enhance the superconducting current transmission capability and increase the engineering critical current density, thus being one of the major routes to reduce the cost of CCs. The “thickness effect”, i.e. critical current density (J_c) decrease with the increase of film thickness, mainly hinders the fabrication of high-quality superconducting thick films. This article introduces the preparation methods and epitaxial growth mechanism of YBCO thick films, discusses various factors that affect J_c and main ways to improve J_c, and summarizes the latest research progress in YBCO thick films by major international teams.