The yield and quality of silage corn are closely related to the harvest time. The plant,ear and grain related silage quality indexes at the stage of 1/2 kernel milk line were studied to provide instruction for determining suitable harvest time and variety selection in silage corn production. The experiments were conducted in Tongzhou experimental base of Beijing Academy of Agriculture and Forestry Sciences in 2018 and 2019. Totally 40 specific silage corn and dual-purpose corn varieties were selected and sampled at the stage of 1/2 kernel milk line. 5 plants for each plot were selected and the fresh weight of stems,leaves,sheaths,ears (without bracts),bracts,rachises and grains of the plant were weighed. The whole plant was baked in 105℃ oven for 30 minutes,and then dried at 60℃ to constant weight,the dry weight was weighed and then used to test the starch content. The result showed that:There were significant differences in the ratios of ear and kernel fresh weight to plant fresh weight(FWe/FWp,FWk/FWp),and that of kernel dry weight to plant dry weight(DWk/DWp) among different silage corn types and varieties at the stage of 1/2 kernel milk line. The ratios of FWe/FWp,FWk/FWp and DWk/DWp for all the tested varieties averaged 30.2%,20.9%,41.1% and ranged 25.5%-35.7%,16.2%-26.4%,33.6%-48.0%,respectively,with the dual-purpose type were 1.5,3.8 and 5.6 percentage point higher than that of specific silage type. The average plant water content of all the varieties was 68.8% (ranged 63.1%-73.6%),with the specific silage and the dual-purpose type was 70.1% and 67.3%,respectively. The average kernel water content of all the varieties was 39.0% (ranged 35.4%-43.6%),with the specific silage and the dual-purpose type was 39.6% and 38.3%,respectively. The average plant starch content of all the varieties was 30.9% (ranged 25.3%-35.6%). JKQZ368 was the highest (32.9%) and DJJ23 was the lowest (25.3%) among the specific silage varieties; JK968 (35.6%) and JNK728(35.6%) were the highest,and MC859 was the lowest(28.3%) among the dual-purpose varieties. The average plant starch content of the specific silage varieties was 29.6%,which 2.9 percentage point lower than that of the dual-purpose varieties (32.5%). At the stage of 1/2 kernel milk line,the average plant and kernel water content of all the varieties was 68.8%,39.0%,and the average starch content was 30.9%; the ratios of FWe/FWp,FWk/FWp and DWk/DWp for all the tested varieties averaged 30.2%,20.9% and 41.1%. During the suitable harvest period,the ratio of FWe/FWp of specific silage/dual-purpose corn varieties was ≥ 30%(the ratio of FWk/FWp was ≥ 20%,and that of DWk/DWp was ≥ 40%),the dry biomass content was ≥ 30% and the starch content was ≥ 30%. So,we suggested that the ratio of FWe/FWp could be used as a simple index for evaluating the quality of silage maize.