In order to reveal the changes of undergrowth shrubs and herbs community structure and diversity after fire of mixed Pinus thunbergiiQuercus acutissima forests understory plant community and explore the relationship between community species distribution and diversity index and soil factors in Jiaodong Hilly Area, we took medium fire, low fire and unburned forest in Weihai burned area as research object. Quantitative soil analysis and plant species diversity surveys were conducted on different firesoiled forests, and the canonical correspondence analysis (CCA) and redundant analysis (RDA) were used to sort and compare the diversity of shrub plants under different fireburning areas. The main soil factors affecting the species diversity of understory shrub communities in different fire areas were also explored. The results show that: (1) the richness, diversity and evenness index of all forestlands presented as herb layer > shrub layer in the vertical direction of the community. The richness, diversity and evenness index of shrub layer rose firstly and then decreased with the increase of fire intensity, reaching the maximum value in the low fire. It is the key transitional period of shrub community characteristic change. The herb layer Patrick, ShannonWiener and Simpson index gradually decreased, and the Margalef index firstly decreased and then slightly increased, reaching the maximum value in the unburned forest, and the evenness index showed no significant difference among the woodlands (P> 0.05). (2) The MoristaHorn index between unburned and medium fire was the smallest in shrub layer, herbaceous layer and shrub layer, with the highest βdiversity, and different composition of undergrowth species. Low and medium fire had higher heterogeneity at shrub level, while unburned and low fire had higher heterogeneity at herb level. (3) Medium fire and low fire understory shrubs and herbs communities can be roughly divided into three groups. The shrub layer and herbaceous layer plants under unburned forest scattered without forming a community. The main positive factors of moderate burning on plant diversity were carbon nitrogen ratio (C/N), and the main negative factors were total phosphorus (TP) and total potassium (TK). The forward factor is phosphorus nitrogen ratio (N/P) and the reverse factor is pH. The species diversity of unburned forest land is affected by a variety of soil factors. (4) Fire increased the rate of species replacement in undergrowth shrub community, increased the species diversity in shrub layer, and decreased the species diversity in herb layer. There are similarities and differences in the factors that affect the species diversity of the community in the fire area. TK and TP are the common influencing factors of plant diversity in the burned area, and P is the common limiting element of plant diversity in the burned area.