Disclosed are a motor variable frequency driving system and a multi-split central air conditioner. The motor variable frequency driving system includes: a three-phase alternating-current input, a rectification module, a thin-film capacitor, an inverter, a vector control module, an A/D sampling module and a steady state processing module. The rectification module is connected to the three-phase alternating-current input; the thin-film capacitor is arranged between output ends of a direct current output; an input end of the inverter is connected to an output end of the direct current output; an output end of the inverter is connected to a three-phase alternating current motor; the vector control module is connected to the inverter; the A/D sampling module is used for collecting direct current bus voltages of two ends of the thin-film capacitor; and the steady state processing module is connected to the A/D sampling module.