The invention discloses a multifunctional photovoltaic UPS (uninterruptible power supply) system and a control method thereof. The multifunctional photovoltaic UPS system comprises a photovoltaic battery, a first switch unit, a second switch unit, a third switch unit, a fourth switch unit, a fifth switch unit, a DC (direct current)/DC (direct current) unit, a storage battery, a two-way DC/DC unit, an inverter unit and a controller unit, wherein the controller unit is electrically connected with the first unit switch, the second switch unit, the third switch unit, the fourth switch unit and the fifth switch unit; and the inverter unit, the two-way DC/DC unit and the DC/DC unit are electrically connected with the controller unit respectively. The multifunctional photovoltaic UPS system is used for controlling the on-off of the first unit switch, the second switch unit, the third switch unit, the fourth switch unit and the fifth switch unit through the controller unit and has the functions of UPS, photovoltaic off-grid generation and photovoltaic grid generation, and the controller unit is used for optimizing work modes of the system, improving the utilization efficiency of photovoltaic resources and exerting utility to the greatest extent.