The invention relates to a multi-inverter module paralleling frequency conversion device for a transmission system and a control policy. The device comprises a rectifier, inverters, a braking device, a cooling system, a protection device, an interface and the like, and is characterized in that an inverter paralleling structure realizes a relatively high power factor; through the parallel connection of multiple rectifying modules and the parallel connection of multiple inversion units, the output capacity of the inverters is increased, and the input / output harmonic waves are reduced; a control box drives a motor to operate by controlling the work of a frequency converter; and a fuse group and control power supply perform fault protection on the system and provide power to each part. In the control policy, a motor driving mode that master and slave modules perform hierarchical control is adopted; as the master control module synchronizes the slave control module, the problem of difficult same-frequency and same-phase output of multiple inverters in the case of motor load is solved; by monitoring the current of each inversion module (multiple inversion modules) and dynamically adjusting the output of each inversion module, the key technology of realizing homogeneous flow of the outputs of multiple paralleling inversion modules is broken through, and an inverter paralleling frequency conversion and speed regulation control method with relatively high static and dynamic performance is realized; and high power of the frequency conversion device with multiple paralleling inversion modules for the transmission system is realized.