Cloud droplet probe plays an important role in activities of weather modification for its high efficiency and simple structure. In this paper, a new cloud droplet probe in which a single-mode 685 nm laser with fiber output coupling was used as a transmitter. A pinhole was used to cut the beam of the laser, so only the central part of the beam which was relatively homogenous illuminated cloud droplets. An embedded computer with two high speed A/D convert chips (10M/s) was used to acquire and process the signal from cloud droplets continually. All the raw data from cloud droplets was stored on the solid disk of embedded computer as well as the calculated size distribution was sent to the master computer in the carbin. By the calibration using standard particles with known index and sizes, the response curve of probe was obtained from which the magnitudes of cloud signal can be changed into sizes of droplets. In the end, the probe was installed on an airplane and field observation experiments were conducted. The results show that this probe is able to measure cloud droplets.