Abstract: There are strict production calculation formulas for simple round formations or linear formations, and the formulas are similar to Ohm’s law. However, it is difficult to calculate the production of complicated formations because there is no analytical formulas, resulting in the difficulties in production management. In order to study the flow of complicated formations, the paper proposes an equivalent flow resistance method which considers a complicated formation as a combination of round formation and linear formation equivalently, then calculates the flow resistance of the complicated formation according to the principle of water-electricity similarity, finally the production formula is established for the complicated formation based on the Ohm’s law. But during the process, there are still some divergences. Some researchers propose to use a larger flow circle, and some others are likely to use a smaller one. Obviously the larger flow circle overestimates the flow resistance and underestimates the flow rate of wells, while the smaller flow circle underestimates the flow resistance and overestimates the flow rate. The influence of the equivalent circle processing method on the calculated production of horizontal wells is relatively small but is significant on the calculated production of vertical wells. The study shows the equivalent processing method of the smaller flow circle is more reliable than that of the larger one. It is suggested that the equivalent processing method of smaller flow circle should be adopted in the study and application of the equivalent flow resistance method