An experimental method for indoor real-time dynamic monitoring of a hydraulic fracture width, comprising the steps of: test piece preparation: assembling a prefabricating mold and fixing a fiber grating therein; mounting a simulated wellbore in the prefabricating mold, pouring agitated cement mortar into the prefabricating mold, and the cement mortar is solidified to form a test piece; mounting the test piece into a confining pressure chamber of a true triaxial hydraulic fracturing simulation device, connecting a liquid injection line to the true triaxial hydraulic fracturing simulation device, and connecting the fiber grating to a modem that is connected to a computer; hydraulic fracture width monitoring test: injecting liquid into the confining pressure chamber of the true triaxial hydraulic fracturing simulation device through the liquid injection line to apply three-direction confining pressures to the test piece, injecting liquid into the simulated wellbore, and starting the fiber grating and the modem to dynamically monitor the hydraulic fracture width in the test piece; and when a hydraulic fracture inside the test piece reaches an outer surface of the test piece, ending the test.