Abstract: To investigate the effect of different sowing dates on stem tiller young ear differentiation and yield of winter wheat in Shanxi Province, the authors took new variety ‘Linfen 8050’ winter wheat as materials, observed the main stem tiller young ear differentiation and yield performance under different sowing dates. The results showed that, with delayed sowing dates and rising tiller site, the dates of ear differentiation were postponed in each period, the total duration was shortened; late sowing treatment had 121 days less in ear differentiation than early sowing treatment. With delayed sowing and rising tiller site, the dates of ear differentiation of each stem tiller were postponed; ear differentiation of late sowing delayed 109 days compared with early sowing. With delayed sowing date, the main stem young ear elongation showed a trend of short-long-short, the duration from elongation to pistil and stamen differentiation was shortened; differentiation after each pistil and stamen differentiation stage had basic synchronization. At the same sowing date (early sowing, the sowing) with rising tiller site, the duration from elongation to double ridge stage differentiation was obviously shortened, and after that, there was little difference in the duration of each differentiation. For late sowing with rising tiller site, the duration of each differentiation increased slightly; but the second and third tiller from the late sowing treatment to floret differentiation stage and the third tiller in sowing died. The effective spikelet number of the main stem and tiller spike decreased obviously with the postponing of the sowing date, the effective spikelet number of early sowing and sowing was 643.58×10⁴/hm² and 601.66×10⁴ /hm², respectively, significantly different from that of late sowing, which was 549.38×10⁴/hm², and yield decreased significantly. Therefore, September 25^th to October 5^th was suitable sowing time of winter wheat in southern Shanxi Province.