A turbidity measuring system for measuring a sample liquid comprising: a chamber with at least one inlet and at least one outlet; a chamber cap for covering the chamber; a sensor unit mounted on the chamber cap, said sensor unit including: a immersion body being placed partially below the liquid surface in the chamber when the sensor unit is in use; a light source; a first light focusing device for focusing a light emitted from the light source and passing therethrough into the liquid sample; a second light focusing device for collecting at least one scattered light resulted from the light passing into the liquid sample; a light detector for receiving the collected light thereby generating electronic signals; and a processor for converting the electronic signals into turbidity measuring units, wherein said immersion body has two cavities (103, 109) for accommodating the light source and the light detector therein respectively, and two cylindrically-shaped channels (104, 105) for accommodating the first and second focusing devices therein respectively, the cylindrically-shaped channels are tilted away from the bottom of said immersion body at an angle symmetrically, and each of the channels (104, 105) has a flat end tilting respectively to its own cylindrical axis with an angle so as to be parallel with the bottom of said immersion body; characterized in that the inlet points toward an analytical area defined by overlapping a first optical path of the light emitted from the light source and then passing through the first light focusing device and a second optical path of said at least one scattered light collected by the second light focusing device, and the immersion body has a tilted bottom with respect to a sample liquid surface of the sample liquid when in use. a chamber with at least one inlet and at least one outlet; a chamber cap for covering the chamber; a sensor unit mounted on the chamber cap, said sensor unit including: a immersion body being placed partially below the liquid surface in the chamber when the sensor unit is in use; a light source; a first light focusing device for focusing a light emitted from the light source and passing therethrough into the liquid sample; a second light focusing device for collecting at least one scattered light resulted from the light passing into the liquid sample; a light detector for receiving the collected light thereby generating electronic signals; and a processor for converting the electronic signals into turbidity measuring units, wherein said immersion body has two cavities (103, 109) for accommodating the light source and the light detector therein respectively, and two cylindrically-shaped channels (104, 105) for accommodating the first and second focusing devices therein respectively, the cylindrically-shaped channels are tilted away from the bottom of said immersion body at an angle symmetrically, and each of the channels (104, 105) has a flat end tilting respectively to its own cylindrical axis with an angle so as to be parallel with the bottom of said immersion body; characterized in that the inlet points toward an analytical area defined by overlapping a first optical path of the light emitted from the light source and then passing through the first light focusing device and a second optical path of said at least one scattered light collected by the second light focusing device, and the immersion body has a tilted bottom with respect to a sample liquid surface of the sample liquid when in use. a immersion body being placed partially below the liquid surface in the chamber when the sensor unit is in use; a light source; a first light focusing device for focusing a light emitted from the light source and passing therethrough into the liquid sample; a second light focusing device for collecting at least one scattered light resulted from the light passing into the liquid sample; a light detector for receiving the collected light thereby generating electronic signals; and a processor for converting the electronic signals into turbidity measuring units, wherein said immersion body has two cavities (103, 109) for accommodating the light source and the light detector therein respectively, and two cylindrically-shaped channels (104, 105) for accommodating the first and second focusing devices therein respectively, the cylindrically-shaped channels are tilted away from the bottom of said immersion body at an angle symmetrically, and each of the channels (104, 105) has a flat end tilting respectively to its own cylindrical axis with an angle so as to be parallel with the bottom of said immersion body; characterized in that the inlet points toward an analytical area defined by overlapping a first optical path of the light emitted from the light source and then passing through the first light focusing device and a second optical path of said at least one scattered light collected by the second light focusing device, and the immersion body has a tilted bottom with respect to a sample liquid surface of the sample liquid when in use.