Nanfu 273-Ping 253 well is an important experimental well in Daqing oil field, which was drilled by whole process unbalanced technology with the target layer of F15 oil reservoir. Unbalanced state was kept at the bottom of the well by downhole casing shut-off valve in whole process unbalanced drilling operation, the oil reservoir was protected by unbalanced drilling and non-snubbing service. The paper introduced the whole process unbalanced technology, well trajectory control, equipment selection, the difficult problems in field and the countermeasures.