To improve the economic optimization response speed of a grid-connected microgrid system and reduce the overall generation operational cost, a second-order neighbor pinning consensus algorithm is proposed. The incremental cost rate (ICR) is defined as a state variable, the power deviation elimination term is introduced to quickly eliminate the total power deviation, and the second-order neighbor term and pin term are used to achieve fast convergence to the optimal ICR. The optimal active output reference value for each distributed generation (DG) is calculated. Then, an economic optimization control method of grid-connected microgrids based on second-order neighbor pinning consensus is proposed. The new method is based on a constructed three-layer distributed hierarchical architecture. The first control layer is a droop control with dual closed-loop feedbacks, the second uses voltage-frequency optimization control to stabilize the system’s frequency and voltage, and the third outputs the optimal active output reference value of each DG to the P/f droop control layer to achieve the economic optimization of the system as well as the balance between load power supply and demand. Finally, a simulation model of the eight-DG parallel operation system is built. The simulation results show that the proposed method can complete the economic distribution of active power output, and the system has excellent response performance. When the system is affected by factors such as sudden load increase, power overlimit, time-of-use tariffs, topology switching, line loss and plug and play, etc., the proposed method can make the microgrid reach the economic optimization state quickly.