In this study, we explore the growth of Bacillus subtilis biofilm on substrates with different agar concentrations, and obtain the area, thickness and morphology information of biofilm by using optical imaging technologies. We find that growth rate variations of biofilms growing on substrates with high and low agar concentration (1.5wt%, 2.0wt%) are not in the same phase, which is because that the interaction between the biofilm and agar substrate on 1.5wt% agar concentration is larger than that of biofilm on 2.0wt% agar concentration, making the growth rate decreases more sharply in the 1.5wt% agar concentration case before wrinkle pattern IV comes up. In the later growth stage after wrinkle pattern IV appears, the biofilm has larger growth rate growing on 2.0wt% agar concentration, that is because the above biofilm has larger wavelength in wrinkle pattern IV reducing energy consumption. Our study shows that the stiff substrate does not always inhibit the biofilm growth, although it does in the earlier stage, after that, mature biofilms acquire larger growth rate by adjusting the growth mode through the wrinkle evolution even in nutrient extremely depletion.