The invention relates to the technical field of air conditioners and provides an air conditioner and a parallel flow heat exchanger thereof. According to the parallel flow heat exchanger, a first liquid storage tank, a first striding pipe and a first pipeline are arranged between a lowest chamber and an uppermost chamber of a flow collecting pipe, wherein one end of the first striding pipe is communicated with the uppermost chamber, the other end of the first striding pipe is communicated with the bottom of the first liquid storage tank, one end of the first pipeline is communicated with the upper portion of the first liquid storage tank, and the other end of the first pipeline is communicated with the lowest chamber. According to the air conditioner and the parallel flow heat exchanger thereof, the liquid storage tank is arranged on the uppermost flow path layer for vapor-liquid separation, refrigerating fluid in a vapor state is separated out before the refrigerating fluid enters a flat pipe at the topmost end of the parallel flow heat exchanger, and it is guaranteed that the refrigerating fluid entering the flat pipe at the topmost end is in a liquid state; as a result, the heat exchanging efficiency of the flat pipe at the topmost end is greatly improved, and therefore the problems that the heat exchanging amount and the heat exchanging efficiency are low due to the fact that the refrigerating fluid in the liquid state cannot be conveyed to the heat exchanging space at the upper end of the heat exchanger at the low frequency are solved.