Huashengyou 21 Simiao is a new three-line hybrid late indica rice variety developed by Hubei Huazhan Seed Technology Co., Ltd. and Jiangxi Xiannong Seed Industry Co., Ltd., using Huasheng A as the female parent and 21 Simiao as the male parent. This variety has suitable growth period, good plant type, moderate plant height, excellent quality (level 1 standard), high and stable yield, and high seed production yield. It was approved by the Hubei Provincial Crop Variety Approval Committee and the National Crop Variety Approval Committee in 2021 and 2022, respectively. The paper introduced the breeding process, characteristics, bey cultivation techniques and seed production techniques of the variety.