As a key component of various acoustic systems, acoustic beam splitter (BS) finds important application in many scenarios, yet are conventionally based on the assumption that the acoustic waves propagate as easily when incident from either input or output side. It would therefore be intriguing, from the viewpoints of both science and technology, to break through this limit by realizing acoustic BSs supporting asymmetric transmission. Here we propose the concept of one-way acoustic BS capable of splitting acoustic beam incident from the input port into multiple beams while effectively reducing the backward transmission from any of the output ports. Furthermore, our design enables flexibly adjusting the number and angle of output beams by blocking the unused line defects. The numerical results verify the theoretical predictions and demonstrate the phenomenon of one-way acoustic BS at the predesigned frequency. Our design with functionality and flexibility bridges the gap between acoustic diodes and BSs and may enable novel multi-functional devices with great application prospects in diverse fields such as acoustic integrated circuits and acoustic communication.