Ordovician deep carbonate rocks have become an important field of natural gas exploration in Changqing. However，compared with the conventional dolomite reservoirs，the Ordovician carbonate reservoirs are deeply buried and tight with high limestone content and fast acid-rock reaction. Conventional acid-fracturing is confronted with short acid-etched fractures and low single-well production. Therefore，it is necessary to study acid-fracturing mechanism and optimize the deep acid-fracturing technique to improve the acid-fracturing effect. In accordance with the reservoir geological characteristics and the demand for acid-fracturing，the kinetic experiments of acid-rock reaction，the evaluation of acid etching，and the numerical simulation of acid fracturing were carried out to clarify the differences in the acid-rock reaction mechanism of carbonate reservoirs with different dolomite contents：With the decrease in dolomite content and increase in limestone content，the acid-rock reaction is accelerated with severer acid etching on the rock surface，while the length of acid-etched fractures witnesses a decline. Hence，the differential design of carbonate reservoirs with different dolomite contents should be strengthened. The deep acid-fracturing technology with the core of“hydraulic fracture generation by prepad fluid，alternative acid injection by multi-system，and internal fracture turning”was optimized based on the idea of“forming hydraulic fractures first and then conducting acid etching”. Through the joint action of acid solution and fracturing fluid，a fracture network connecting hydraulic fractures，acid-etched fractures，and matrix dissolved pores was formed. In the field test，our technology has played a role in raising production.