Borehole stability is a key problem in complex formation drilling. According to the analysis on ABD-1 compound drilling fluid that bases mainly on asphalt, plastic asphalt can expand 5～7m in the fissure of 0.5～16cm, but only 1m in the smaller cranny. Field application was made on ABD-1 compound drilling fluid assisted by surfactant and bentonite, more than 430m drilling in sand and mud layer was completed.