The invention discloses an off-line detection device and measurement method for ice nuclei concentration and ice-forming activity in the mode of infiltrating nuclei, comprising: a liquid separator, a PCR plate, a PCR bracket, a water bath, a computer, a lens, and a CCD camera; Temperature control, temperature recording, picture acquisition and data processing modules; the PCR plate is placed on the PCR support, and together with the PCR support is placed in the condensate in the water bath; the water bath and CCD camera are connected to the computer; through picture collection The module controls image acquisition, image storage, and data processing. The invention realizes that the liquid holding tank can hold more liquid droplets; reduces the loss of particles to be tested; adopts the PCR board to reduce the problem of mutual influence of liquid droplets in the cooling process, increases the volume of liquid droplets that can be measured, and reduces the The difficulty of liquid, reducing the error caused by inaccurate quantification of droplet volume. The invention is easy to operate, and can simultaneously perform temperature recording, image acquisition and data processing.