Multi-connected air conditioning system and defrosting control method thereof

The invention discloses a multi-connected air conditioning system and a defrosting control method thereof. The multi-connected air conditioning system comprises an indoor unit module and a plurality of outdoor unit modules connected in parallel, wherein each outdoor unit module comprises a compressor, a four-way valve, an outdoor heat exchanger, a first throttling element, a first control valve, a second control valve, a third control valve, a fourth control valve, and a fifth control valve; each first control valve is connected between the corresponding first throttling element and the indoor unit module; each second control valve is connected with the corresponding first throttling element; and each second control valve is connected to a first public pipeline; each third control valve is connected with a corresponding fourth control valve port; each third control valve is connected to a second public pipe; and the second public pipe is connected with the indoor unit module; each fourth control valve is connected with a second valve port and the first public pipe; each fifth control valve is connected with a first valve port and the second public pipe. According to the invention, continuous heating during defrosting is realized, and the indoor unit module does not stop, so that comfortability is improved.