Abstract: Small mixing cloud chamber with liters cubage has been used in the observation of the nature ice nuclei and the detection of the nucleating effectiveness of artificial ice nuclei. Practical usage shows that the testing data are different due to various cubage and methods of supplying fog as well as operation procedure which lead to the difficulty to compare the results. A 15-liter mixing cloud chamber is developed to improve the creditability of data and test the ice nuclei effectiveness of "the 37 model silver iodide shell". The cloud chamber is cooled by a F22 refrigeration system.The lowest temperature within cloud chamber is down to-28℃.In order to keep the temperature stable, a jacket tank filling with glycol-water solution is designed at the cloud chamber periphery. In the glycol-water solution, a 1 kW electric heater is installed to adjust the temperature.Outside the jacket tank, a 10 mm thick cold insulation is made using frothing technology to ensure heat insulation. When the cloud chamber runs, the experiment temperatures are obtained by controlling the cooling compressor and the electric heater. In addition, a device is developed to collect ice crystals with two methods so that to extend the detect range of the ice nuclei concentration. Glass slice is used by one of the methods to collect ice crystals and then the ice crystals are counted by a microscope, sugar plate is used by another method to collect ice crystals and then they are counted by naked eye. The two methods can be used alternatively according to the needs in experiment. The former is often used if the ice nuclei effectiveness is high (cloud seeding agents) and the latter can be used at low concentration (natural ice nuclei). Another important improvement is that the super-cooled fog can be supplied to ensure the nucleation full of the ice nuclei in cloud chamber. At first fog with normal temperatures is generated by an ultrasonic atomizer and passes through a low temperature narrow access so as to arrive at supercooled degree. And then it enters the chamber after the temperature of super-cooled fog equals or is under the mid temperature of cloud chamber. Thus the effect of instantaneous high super-saturation is avoided in this technology and the temperature is not disturbed. In order to improve the ice nuclei effectiveness of the cloud seeding agents carried by shell, several composite formulations are tested with the cloud chamber. The results show that the cloud chamber has a better stability and reproducibility than other small mixing cloud chambers. The better performance should be ascribed to the design of supplying super-cooled fog and the improvement of ice crystals collecting method.