RADEX non-LTE modeling of the relation between the kinetic temperature and the average ratio of H₂CO 3₂₂−2₂₁/3₀₃−2₀₂ and 3₂₁−2₂₀/3₀₃−2₀₂ with an assumed density of n(H₂)=10⁵ cm⁻³ and column densities N(para-H₂CO)=1.0× 10¹³, 6.6 ×10¹³, and 1.0×10¹⁴cm⁻² (red, green, and blue), the LTE (cyan), and an averaged line width of 3.8 km s⁻¹. The LTE kinetic temperature (T_LTE) was determined using the methodology described in Mangum & Wootten (1993) and Tang et al. (2017b). T_LTE is calculated as $T_{\text{LTE}}=\frac{47.1}{\ln (0.556/\text{ Ratio })}\text{\hspace{0.17em}\hspace{0.17em}K}$, where Ratio represents the average ratio of H₂CO 3₂₂−2₂₁/3₀₃−2₀₂ and 3₂₁−2₂₀/3₀₃−2₀₂. The black points are derived from our observed H₂CO line ratios from the DR21 filament for a column density N(para-H₂CO) = 6.6 × 10¹³ cm⁻². The temperature uncertainties are obtained from observed H₂CO line ratio errors.