Flowering phenology is considered as an important fitness factor because it plays a crucial role in reproductive success. Hypecoum erectum is an ephemeral psammophyte with fragmented distribution in the Gurrbantuggut Desert of Xinjiang, China. Our aim is to investigate the flowering phenology of H.erectum and to better understand its reproductive features. The study was conducted in Cainan oil field which is located at the southern edge of the Gurbantunggut Desert. We selected 30 H. erectum individuals with more or less height and crown diameters in the wild population and randomly marked three inflorescences on each individual and observed them from April to June in 2015. We observed the flowering course of each individual including the first flowering date, duration, mean flowering amplitude and last flowering date and then calculated relative flowering intensity and synchrony indices. We also analyzed relationships between first flowering date, median date, duration, last flowering date, flowering amplitude and flowering synchrony, the correlation matrix between first flowering date and duration, flower number and fruit set. According to the external petal opening situation and dehiscence, the typical single flowering process for a flower can be divided into four stage, we observed the four stage of single flower including external petal color changes, the relative position of the median lobe and anthers, the pollen quantity changes in median lobe, the relative position of the stigma and anthers, the relative position of the median lobe and stigma, stigma dehiscence, and the situation of anther dehiscence. The results showed that: (1) The flowering span of the population and individual was approximately 36 d and 16 d from the late April to late May. (2) The flower numbers of the individual and inflorescence was approximately 107±60 and 10±4. The single flowering span can be divided into four stages based on the dehiscence situation of the outer petals and stigma. The single flower of H. erectum has delicate petal structure with double petals. The inner petals are composed of a median lobe and a lateral lobe. Each flower has four anthers. H. erectum exhibits a “massflowering” pattern. (3) The synchrony index was 0.748. The relative flowering intensity had two major peaks from 20% to 30% and from 50% to 70% and the skewness was 0.45. (4) Correlation analysis among the first flowering date, flowering duration, flower number, and fruit number showed that there was significant negative correlation between first flowering date and flowering duration, and there was significant positive correlation between flower number and fruit number. (5) In the natural treatment, the percent fruit set was 82.7%±0.1% and the percent seed set was 93.6%±0.8%. The two major peaks in relative flowering intensity may be a strategy to attract pollinators and increase the number of seeds to ensure reproductive success.