An automatic magnet assembling mechanism of a magnetic sheet building block toy comprises a bottom case feeding mechanism, a first rotary mechanism, a second rotary mechanism, a magnet assembling mechanism and a pressing mechanism. The first rotary mechanism and the second rotary mechanism are adjacently arranged, and the bottom case feeding mechanism, the magnet assembling mechanism and the pressing mechanism are all arranged beside the first rotary mechanism. A discharging mechanism is arranged beside the second rotary mechanism, and a conveying mechanism is arranged between the first rotarymechanism and the second rotary mechanism. The first rotary mechanism comprises a first rotary motor and a first rotary disc, and the first rotary disc is mounted at the output end of the first rotary motor. A plurality of first jigs distributed circumferentially are arranged on the first rotary disc. The second rotary mechanism comprises a second rotary motor and a second rotary disc, the secondrotary disc is mounted at the output end of the second rotary motor, and a plurality of second jigs distributed circumferentially are arranged on the second rotary disc. A discharging hole is formedin the middle of each second jig. Automatic magnet assembling of magnetic sheet building blocks can be achieved.