Abstract: It has been proven that the volcanic formation in eastern Changyuan of Daqing has special lithology and pore characteristics, and can be easily contaminated during drilling and later stimulations, thus causing formation damage and leading to low production capacity. In 1998, Under Balanced Drilling (UBD) technology was used in this area to evaluate the production potential in the volcanic formation of Yingcheng formation, aimed at improving production capacity and realizing a breakthrough in such formations. Detailed research methods was illustrated and a set of UBD technologies suitable for the volcanic formation were formed, which consist of designing of reasonable casing program, proper BHA and drilling parameters, predicting of gas migration, annular mud weight and pressure distribution, as well as downhole pressure controlling, etc. Field UBD operations and the results were also presented.