Abstract: Pulsating hydraulic fracturing technology has demonstrated advantages such as lower initiation pressure and complex fracture networks in reservoir stimulation fields including gas extraction, shale gas development, and geothermal exploitation. Currently, the method of controlling flow rate to achieve pulsating hydraulic load output is commonly used in engineering, but the mechanism of fracture propagation remains unclear. To address this, true triaxial flow-controlled pulsating hydraulic fracturing experiments were conducted on sandstone specimens to analyze the effects of pumping frequency and rate on injection pressure, acoustic emission energy, fracture type, and macroscopic fracture morphology. The results indicate that the initiation pressure, breakdown pressure, and transient energy of flow-controlled pulsating hydraulic fracturing increase with the increase of pumping frequency and rate, while the fracture propagation area decreases with increasing pumping frequency and initially increases then decreases with increasing pumping rate. Compared to conventional hydraulic fracturing, the acoustic emission energy is more concentrated, the initiation pressure is lower, with a maximum reduction of 21.9%, the proportion of shear cracks increases by 5.6% to 17.8%, and the fracture propagation area can increase up to 2.3 times. The pulsating hydraulic load varies complexly, showing a ramp-shaped load with fixed frequency, increasing pressure mean and amplitude during the initiation phase, and a horizontal cyclic load with fixed upper pressure limit, frequency, and amplitude during fracture propagation. The upper, lower, and mean pressure limits are positively correlated with pumping frequency and rate, while the pressure amplitude is negatively correlated with pumping frequency and initially increases then decreases with increasing pumping rate. Different types of output pulsating hydraulic loads result in significantly different fracture propagation characteristics. To enhance fracturing effectiveness, the design of fracturing parameters must ensure that the output pulsating hydraulic load has sufficient strength and amplitude.