In BB131 datasheet， I find the difference between min capacitance and max capacitance at same voltage （28V）is so big in Fig.1. But, i calculate refer to the Fig.2 and Fig.4, the result fromCalculation of the effect of temperature on the capacitance is so small，only 0.5pF. So,Why is the difference so large.

The min/max values in the table "LIMITING VALUES" represent production variance.

Figures 2 and 4 show changes of the capacitance and temperature coefficient for typical device. These figures do not include production variance.

Figure 2 represents a curve for a typical device with Cd=12.8pF @ 0.5V.

Suppose, you got a device with Cd=8pF @ 0.5V then it's Cd curve should be a scaled version of Figure 2, just multiply all Cd values by 8pF/12.8pF.