Fracturing and imbibition was the main method to extract matrix crude oil of ultra-low permeability reservoirs. But the oil recovery rate of water imbibition was lower than economic need，while using the surfactant combination could improve the imbibition recovery factor. The influence rules of the combined surfactant system on the imbibition recovery of ultra-low permeability reservoirs were discussed by performance analysis. For the anionic surfactant HABS，nonionic surfactant APG1214 and their combination system，the osmotic bottle test was used to determine the imbibition recovery. The effects of three factors on oil recovery rate including interfacial tension between oil and formation，contact angle of cores before-and-after soaking in surfactant and the stability of emulsion were analyzed. The results showed that the imbibition recovery rate of the compound system was the highest one（10.43%），that of HABS and KCl system was 4.57% and 2.2%，and APG1214 system couldn’t extract oil by imbibition.The interfacial tension（IFT）between combination system and oil could reach 10-2 mN/m. The combination system could exchange the wettability of cores from hydrophilic to weak hydrophobic which contact angle was nearly 90o，and the system was easy to form emulsion which was easy to coalesce. In the displacement experiments，the injected pressure of combined system was the lowest one and the enhanced oil recovery rate was the highest one. Lower IFT，intermediate-wet reservoir and unstable emulsion were favorable conditions of imbibition，while the emulsion with extremely high stability was helpless.