Hydro cyclone

A hydro cyclone applying for separating a supernatant solution is provided. The water cyclone separator has a body, a feeding part, an overflow part and a bottom-flow part. The body has a first upper part, a first lower part connected to the first upper part, and a space inside the first upper part and the first lower part. The first upper part has a top surface and a lateral surface, and the first lower part is tapered from the first upper part. The supernatant solution passes the feeding part, disposed at the lateral surface and connected to the space, into the space. The overflow part traversed the top surface and connected to the space has a second upper part, exposed from the top surface, and a second lower part, sited in the space and tapered from the second upper part. The bottom-flow part is connected to the first lower part and the space.