In order to explore the reason for flower formation of Malus halliana var. parkmanii, this study took single and double petaled M. halliana as experimental materials, and observed the flower organ differentiation process of singlepetaled and doublepetaled M. halliana by means of stereomicroscope and scanning electron microscope; The flowers in bud stage and blooming stage of M. halliana var. parkmanii were observed anatomically, and the morphology and number of flower organs were counted; The R was used to analyze the correlation between the number of petals of M. 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 doublepetaled M. 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, M. halliana only differentiated one round of 5 petals primordia evenly distributed at the junction of two sepals. However, M. 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 M. 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 M. 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 results showed 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 M. halliana var. parkmanii.