The invention belongs to the technical field of dynamic stability analysis of new energy power systems, and particularly relates to an electromechanical oscillation mode estimation method of a power system based on aggregation models of large-scale wind power plant and photovoltaic power station. The method comprises the steps as follows: firstly, a transfer function model of a single direct-drive fan or a photovoltaic power generation unit is established; the aggregation models of the overall wind power plant and photovoltaic power station can be obtained by a method for directly multiplying the model of single power generation equipment or a method for reducing orders after addition; for the wind power plant or the photovoltaic power station with unknown parameters, the aggregated transfer function model is obtained through a field frequency response test; and an electromechanical oscillation mode of the power system is estimated by adding an open-loop characteristic value of the system to the product of the aggregated transfer function value and the residual error. According to the electromechanical oscillation mode estimation method, the model order and the computation complexity are greatly reduced under the condition of ensuring certain accuracy, so that the help is offered for small-interference oscillation stability analysis of the power system after new energy generating power supply is connected.