Abstract: An improved diffusion chamber using filter technique has been developed for detecting atmospheric ice nuclei. A movable partition board between the chamber top and bottom plate is designed in order to cut off the vapor source before and after the filter samples being produced. By using a relative stable AgI aerosol source, the examination tests of the chamber responding to ice nuclei concentration have been conducted with various sampling volume filters and under different temperatures. The ice nuclei concentrations have been measured using this equipment and the average daily variation in wintertime at northwestern suburb of Beijing has been given. All these results show that the diffusion chamber will be useful for the study of cloud and precipitation physics.