Radio waves and ultrasound cannot be directly seen by eyes, so the traditional phased array technology demonstrations are mostly animation demonstrations or Matlab simulations. In this paper, a 51 MCU and 3D printing technology are employed to design and produce an experimental instrument for phased array technology demonstration by water waves. The 51 MCU is used to control the time interval which determined the phase difference of the adjacent wave sources. The experimental instrument can be used to visually demonstrate the principle of phased array technology and interference phenomenon, which solves the problem that there is no experimental instrument to demonstrate the phased array principle in classroom. It can also be used to measure wavelength, wave speed, and the deflection angle of a line wave.