The invention relates to the technical field of cyclone application, in particular to a multi-parallel cyclone unit with an online sampling device and an online sampling method. The multi-parallel cyclone unit comprises a support, a distribution cylinder is arranged in the middle of the support, a feeding port is formed in the lower end of the distribution cylinder, multiple parallel cyclones arearranged on the distribution cylinder, feeding pipes of the cyclones communicate with the side wall of the distribution cylinder through distribution branch pipes, and distribution sampling valves arearranged on the distribution branch pipes. The multi-parallel cyclone unit is characterized in that each distribution sampling valve is composed of a valve body, a sealing ring, a gate plate, supporting rods, an air cylinder, a piston, a solenoid valve and an air source, wherein the solenoid valve is arranged to be a three-position five-way solenoid valve, an A position sensor, a B position sensor and a D position sensor are sequentially arranged on the outer wall of the air cylinder from top to bottom, and the inflation and deflation volume of the solenoid valve is controlled through a controller to adjust the opening amplitude and position of the gate plate in the valve. The multi-parallel cyclone unit has the advantages of being simple in structure, capable of achieving convenient online sampling, good in sampling effect, high in sampling efficiency and the like.