The ice nucleation effectiveness for several AgI-type seeding agents in common use in weather modification of China is compared. The ice nucleation mechanisms responsible for various cloud chambers and the error origins of the mixing cloud chamber are analysed. In addition, the measuring results of two seeding agents released with airflow are discussed also. The results show that the detection of AgI-type seeding agents should be regard to the environment as ice nuclei released besides the conditions of the ice nuclei activation should be better simulated by cloud chamber. It is pre-requisite to build testing equipment that could simulate the ventilation, and the test results would be more close to practice in this way.