Abstract: Carbonate reservoirs in the Shunbei Oil and Gas Field are characterized by ultra-deep, high temperature and high fracturing pressure gradient, which pose problems in short acid-etched fractures and rapid conductivity decline. In order to solve these problems, a team studied a deep penetration acid-fracturing technology for ultra-deep carbonate reservoirs, and they proposed a deep penetration acid-fracturingtechnique. Using a synthetic acid thickener and high temperature corrosion inhibitor, a high temperature resistant clean acid was developed. The acid fluid non-uniform etching conductivity test was carried out, and fracture conductivities with clean acid, gelled acid, and clean acid followed by gelled acid were analyzed at a closure stress of 20–90 MPa, respectively. The mechanism of the non-uniform displacement of acid fluid was studied, and the acid-fracturing process parameters of non-uniform etching were optimized. The study suggests that "clean acid + gelled acid" combined injection can greatly improve the conductivity of acid-etching fractures as well as nearly doubling effective fracture length. This new deep penetration acid-fracturing technology has been applied in 5 wells in the ultra-deep carbonate reservoir in Shunbei Oil and Gas Field. The success rate and effectiveness of the acid-fracturing operation reached 100% with post-frac production rate 107.7 m³/d, and average length 133.20 m. Consequently, this acid-fracturing technology can greatly improve the acid-fracturing effect in ultra-deep carbonate reservoirs, which provides a reference or best practices guidance in the acid-fracturing stimulation of similar reservoirs in China.