Abstract: The erect panicle type variety Liaojing 5, Liaojing 454 and curved panicle type variety Liaoyan 16 were chosen to study the seed-setting rate (SR) and its relationship with source and sink by reducing source or sink. The results indicated that significant differences of SR exist among the varieties, the SR of Liaojing 5 is lower than that of Liaoyan 16, but Liaojing 454’s is higher than Liaoyan 16’s; SR varies along the panicle axis, the SR of the upper part is higher than that of the lower part, the SR of primary branch (PB) is high and uniform along the panicle axis, and the SR of secondary branch (SB) is mostly low; source reduced, SR fell, the SR of Liaojing 5 and Liaoyan 16 fell distinctly after being clipped flag leaf, whereas SR rose by clipping half the 1st or 2ed below the flag leaf; sink reduced, SR rose, by clipping PB of certain part of the panicle the SR of SB of corresponding part and total panicle rose evidently; SR of different part of the panicle axis, PB and SB respond diversely to treatment of source and sink, the lower and middle part of the panicle axis were more sensitive than the upper part, and SB were more sensitive than PB, Liaojing 5 has the most visible trend.