The invention provides a variable-diameter drill bit stabilizer for an engineering driller.The variable-diameter drill bit stabilizer comprises a stabilizer central body, a first rolling bearing and a second rolling bearing, wherein the stabilizer central body is sleeved with the first rolling bearing and the second rolling bearing, a plurality of groups of swing arm structures are hinged to the first rolling bearing and the second rolling bearing, each group of swing arm structures comprises an upper supporting arm, a lower supporting arm and a guide shoe plate, both one end of the upper supporting arm and one end of the lower supporting arm are hinged to the guide shoe plate, and both the other end of the upper supporting arm and the other end of the lower supporting arm are hinged to the first rolling bearing.A pin hole is formed in the middle of the lower supporting arm, the lower supporting arm is hinged to the upper end of an ejection rod through the pin hole, the lower end of the ejection rod is hinged to a third rolling bearing, the stabilizer central body is sleeved with the third rolling bearing, the third rolling bearing is fixedly connected with an oil cylinder, and the oil cylinder is fixedly arranged on the outer side of the stabilizer central body.The contact area between the drill bit stabilizer and the hole wall can be increased to keep the drill bit stabilizer stable.