This paper aims to improve efficiency of removal of sand with less water consumption. The scheme is to set a bypass involve a hydraulic cyclone on bottom of the water tank for sand removal. The hydraulic cyclone of Φ50mm with unconventional small range of underflow diameter (1-4mm) were selected to investigate the sand removal performance. The overflow flows back to the water tank and its running is under an intermittent control which depends on the condition of sands accumulating. The experiment focus on the relationship between underflow diameter and underflow productivity as well as split ratio, keeping other operating and geometry parameters to be constant in their conventional range. The result shows that the underflow productivity and the split ratio reach their maximum and minimum respectively when the underflow diameter is nearby 2 mm. It means that there's an optimum underflow diameter for sand removal and water saving. After applying the hydraulic cyclone with 2mm underflow diameter to an experiment system with the inlet pool's volume of 68.7L for 30 minutes, it can achieve the sand removal rate of 90% and consume merely 1.75% of the total water of inlet pool, which reach the target of saving water and removing sand.