“To be lower than” in Chinese is 低于 (dīyú).
温度计往往低于零度。
Thermometers often go below zero.
Example sentence from Tatoeba (CC BY 2.0).
Not to be confused with: 地域 (dìyù, area) · 地狱 (dìyù, hell; underworld; (Buddhism) Naraka) · 抵御 (dǐyù, to resist)