The invention relates to a special water clarifier of a turn back flow water fountain, which comprises an upper cover, an upper barrel and a lower barrel. The bottom of the lower barrel is provided with a float valve or a ball cock which can control the water level in a water hopper of the water fountain, the bottom of the upper barrel is provided with an upper filter element which is provided with an exhaust pipe, a lower filter element is arranged under the bottom of the upper barrel, the bottom of the lower filter element is connected with a turn back flow filter element which includes a shell body with a closed bottom, a lower screen is arranged at the lower part in the shell body, an upper screen is arranged at the upper part in the shell body, and granular filter material is filled between the lower screen and the upper screen. The special water clarifier has the beneficial effects that: firstly, the exhaust of the filter element is reliable, gas in the turn back flow filter element needs to be exhausted when the turn back flow is started for the first time only, so the yielding water of the water clarifier is reliable; secondly, the water filtering power of the water clarifier is enough, the lower filter element adopts micropore ceramics with higher filtering precision, so the filtering effect is increased; thirdly, because water flows through the upper filter element, the lower filter element, and the turn back flow filter element for being purified and treated repeatedly, the water quality of the yielding water is ensured more easily.