Abstract: Under the condition of 450 kg/hm2（26-10-15） slow release fertilizer, the effects of topdressing on grain structure and yield of late rice in different periods were studied. The results showed that compared with direct seeding, the effective spike decreased, the grain number and thousand grain mass increased, and the yield was similar. The maximum yield was achieved by topdressing at the end of tillering and jointing stage（July 15-20）. At tillering stage（June 9 to July 9）, the effective ear of topdressing increased, the ear type was smaller, and the yield was the lowest. Topdressing at the differentiation stage of young ear reduces the effective ear and affects the yield. With the delay of topdressing time, effective ear decreased, ear type increased and yield increased. Topdressing at the differentiation stage of spikelets（August 15） resulted in the largest spike type and highest yield. At the end of tillering（July 20）, the effective ear was the largest and the ear type was small.