In order to explore the reason for flower formation of Malus halliana var. parkmanii, this paper took single - and double - petaled Malus halliana as experimental materials, and observed the flower organ differentiation process of single-petaled and double-petaled Malus halliana by means of electron microscope and scanning electron microscope; It mainly dissected the flowers in the big bud stage and the flourishing stage of Malus halliana var. parkmanii to observe the abnormality of its flower organs; The R was used to analyze the correlation between the number of petals of Malus halliana var. parkmanii and the number of floral organs of other circles. The results were as follows: 1. The floral organ differentiation of single - and double - petaled Malus halliana can be divided into sepal primordium differentiation, petal primordium differentiation, stamen primordium differentiation and pistil primordium differentiation, each floral organ differentiated and developed in a centripetal order. 2. In the differentiation stage of petal primordium, Malus halliana only differentiated one round (5) of petal primordium evenly distributed at the junction of two sepals. However, Malus halliana var. parkmanii differentiated two rounds of hashed petal primordia, with 5-7 in the first round and 7-10 in the second. 3. In Malus halliana var. parkmanii, there are many cases of sepal petalization, stamen petalization, and abnormal development of pistil and stamen. 4. The correlation analysis of the number of floral organs in each cycle of Malus halliana var. parkmanii showed that the number of petals was positively correlated with the number of stamens and the number of stamens in petrification. This phenomenon is different from the phenomenon that the number of stamens decreases and the number of petals increases in the conventional stamen petalization plants. These conclusions show that the increase of the number of petals was not completely dependent on the stamen petrification, which revealed the diversity and complexity of the reasons for the formation of Malus halliana var. parkmanii.