The traditional experimental method of reservoir rock wettability evaluation is not suitable for shale samples. Based on the Yang-Joubi principle, this paper established a three-phase contact angle method of oil–water–shale wettability measurement, which has the characteristics of intuitive detection results and easy quantitative evaluation. The wettability of Gulong shale samples in Songliao Basin was tested by this method. The effects of roughness and maturity Ro on the wettability of shale were evaluated, and the wettability relationship between fracturing fluid and shale was analyzed. The results show that the wettability of both oil-wet core and water-wet core changes towards intermediate wettability with the decrease of sample surface roughness. The wettability of medium and low maturity shale is mainly water-wet, and with the increase of maturity, the wettability changes to oil-wet direction. The contact angle between G1 fracturing fluid and shale is lower, which is more conducive to the oil discharge of fracturing fluid.