The seeds often suck on the sucking hole when the sucking plate rotates. The area between the sucked seeds and sucking hole is smaller than the area between the normal sucked seeds and sucking hole, which leaded to a shortage of suction. As the suction is less than a sum of external forces, sucked seeds will be separated from the seed sucking hole and do a parabolic movement with a particular velocity. This phenomenon is called “early dropping seeds”. To avoid this and increase the stability of seed sowing and the performance of hill formation of rice pneumatic metering device, a shield device was designed. Shield device was fixed on seed chamber shell through bolted connections. It was able to stop the seeds flying to the second half of sucking process after the parabolic movement drove by “early dropping seeds”. Indic hybrid peizataifeng was taken as research subjects, of which the water content was 21.1%. “Early dropping seeds” phenomenon was observed by means of high-speed photography technology, which enabled moving process of sucked seed to be clearly photographed. The probability of “early dropping seeds” was studied by using multi-factor experiment under different negative pressures for seeds sucked, rotation rates and shield device. Precision of seed metering was also counted, as shield devices were installed on the metering device. The experimental results showed the “early dropping seeds” phenomenon and precision of seed metering were improved with a shield device. The optimized condition was that the sucking plate rotation speeds of 25~40r/min and the negative pressure for seeds sucked of 1.6kPa. The probability of 1~3 seeds was 93%~97%. In the experiment, a shield device on the metering device could control the “early dropping seeds”, and improve the stability of seed sowing and the performance of hill formation.