Universal learning machine is a computing system that can automatically learn any computational task with sufficient data, and no need for manual presetting and intervention. Universal learning machine and universal learning theory are very important research topic. Many disciplines (AI, AGI, machine epistemology, neuroscience, computational theory, mathematics, etc.) cross here. In this article, we discuss the principles, methods, and engineering models of universal learning machine. X-form is the central concept and tool, which is introduced by examining objective and subjective patterns in details. We also discuss conceiving space and governing space, data sufficiency, learning strategies and methods, and engineering model.