In order to explore the patch effect of plant diversity in urban remnant mountains (URMs), the URMs in Guiyang city were taken as the research objects, one-way ANOVA and least significant difference method (LSD) were adopted to compare the difference of plant diversity in different URMs and their slope directions and positions. Spearman correlation analysis was used to analyze the patch effect of plant diversity in URMs. The relationship between plant diversity index and patch index was analyzed. The results showed that:except surface roughness (SR) and fractal dimension (Fd), the difference of the remaining patch characteristic indices of patch area (Pa), surface area (Sa), patch shape index (PSI), fragmentation (F), relative height (Rh), average slope (As), horizon curvature (Hc) and profile curvature (Pc) among 23 URMs were larger; The diversity indices of the whole plants, tree layer, shrub layer and herb layer were significantly different in different URMs. All plant diversity indices were correlated with the patch characteristic indices of F, Hc, Pc, Hc, Pa and Sa, but not with Rh, Fd, SR, PSI and As; The order from strong to weak of response intensity of plant diversity indices to URMs patch characteristic indices in different slope positions was the mountaintop, foot of mountain and mountainside. The order from strong to weak of response intensity of plant diversity indices to URMs patch indices in different slope directions was western slope, northern slope, southern slope and eastern slope. In general, there is the patch effect of the plant community diversity of URMs, and the patch characteristic indices of F, Hc and Pc of URMs have a significant impact on plant diversity. The results could provide theoretical and scientific basis for the protection of URM habitats and planning and management of urban green space ecosystem in mountainous cities.