Abstract: The early flowback history data of fracturing fluid can be used to evaluate multi-stage fracturing effect for horizontal wells, and the effective fracture pore volume is a critical parameter to reflect the fracturing effectiveness. However, current calculation methods of effective fracture pore volume based on the fracturing fluid flowback history shows low accuracy. This paper presents a new method for quantitatively calculating the effective fracture pore volume based on flowback history. On the bases of the latest methodology in North America, the method uses the flowing material balance method of rate transient analysis (RTA) and is combined with a traditional production decline method. Its calculation and analysis process is introduced in detail based on a domestic multi-stage fracturing horizontal tight oil well. The calculation results show that only 21% of the injected fracturing fluid contributes to the fracture conductivity. The results show that the new method can effectively improve the calculation accuracy of the effective fracture pore volume and implement correct evaluation of multi-stage fracturing effect for horizontal wells.