To solve the problems such as high-rate reaction with rocks, strong corrosion and environmental pollution of conventional acid fluids in acid fracturing of high temperature and deep reservoirs, an environmental-friendly crosslinked acid (EAC-1) with heat resistance was prepared by solution blending method with lactic acid, gluconic acid, polyethyleneimine (PEI) and thickener acrylamide polymer as raw materials. The synergistic mechanism of CaCO3 dissolved by complex acid with lactic acid and gluconic acid, rheology, microstructures and gel breaking properties of crosslinked acid (EAC-1) were analyzed by FTIR, rheological test and SEM, etc. The reaction rate constant and reaction kinetic equation of crosslinked acid were also determined. The results showed that when the molar ratio of lactic acid to gluconic acid was 1:1, lactic acid and gluconic acid could form a high-solubility chelate with Ca2+ through covalent bond, and no secondary precipitation happened in the residual acid. The viscosity of crosslinked acid could maintain above 50 mPa·s at 170 s-1 and 110℃; the three-dimensional network structure in acid fluid formed by PEI and thickener improved the temperature and shear resistance. The crosslinked acid was broken evenly without residues, and the viscosity of gel breaking fluid was 4.2 mPa·s. The reaction rate constant of EAC-1 was at least one order of magnitude less than that of HC-1 with hydrochloric acid as the main acid, showing that crosslinked acid (EAC-1) had good retarding effect for prolonging the effective action distance of acid fluid in acidizing fracturing.