Acid fracturing is the key production and stimulation technology for the carbonate reservoirs. Ultra-deep horizon? tal wells should be reformed through staged acid fracturing for their complex well conditions. Mechanical packer acid fracturing technology is limited and cannot be used in the ultra-deep horizontal wells due to the influence of well depth and structure. A new type of biodegradable fiber temporary plugging agent has been developed to ensure the success rate and stimulation effect of these wells. Performance evaluation indicates that the new agent has great dispersion and degradation performance，and the diverting and plugging effect is obvious；in the meanwhile，a composite acid fracturing technology has been put forward. By the end of June 2014，10 wells have been treated with this technology achieving 3-10 MPa increase in flow pressure，80% of efficiency，and 1.75-6.1 times of stimulated production. The gas production rate after treatment is about 50×104 m3/d and some are higher than 100×104 m3/d，which indicates significant stimulation effect. Laboratory experiment and field tests both confirm that this technology can realize effective stimulation in the ultra-deep horizontal wells with strong heterogeneity and developed fractures. The treatment process is simple with low operation risk and great adaptability. So it is recommended to apply widely.