In order to improve the effect of artificial rain enhancement, an aircraft equipped with the Particle Measuring System (PMS) probed the spring precipitable stratiform clouds over Northwest China on May 28,2001. The micro-structure characteristics of the cloud system are analyzed by means of micro-physical data from the aircraft measurement,satellite cloud picture and synoptic background data, etc. The main results are as follows:(1) The super-cooled water occurred in a wide temperature range, which is favorable for artificial rain enhancement. (2)In this case, the average particle diameter is about 10～20μm, the average particle concentration is 18.3cm^-3 ,and the average liquid water content is 0.036 g·m^-3 , which is similar to the value of Xinjiang, Hebei, and Shandong Provience, etc. (3) From the 2D image we can see that the coagulation and sublimation are the main processes for ice crystal growing.