Abstract: The main pay zone of M oilfield in Middle East is a carbonate reservoir with middle-high porosity and low permeability. Acidizing is the main technique for carbonate stimulation. Abundant fissure-caverns lead to strong heterogeneity, large amount of acid filtration loss and limited acting distance of acidizing treatment. It is necessary to combine the techniques of slow speed and temporary blocking to increase acidizing depth of heterogeneous reservoirs. Aiming at the reservoir characteristics of the oilfield, this paper evaluated and comprehensively compared the properties of the main retarded acid systems (gelling acid, diverting acid, crosslinking acid, emulsifying acid and chelating acid) of the carbonate rocks, and preferred the diverting acid system. The diverting acid system has been applied to more than 30 wells in this oilfield. After operation, the average oil rate increase of each well is 200 m³/d, and the stimulation effect is remarkable.