The numerical and experimental processes of frost formation on square-finned tubes in natural convection are investigated in the current study. The frost growth survey on these types of finned tubes is beneficial and necessary to understand heat and humidity control phenomena due to low operating temperature. By using cooling, heating, and humidification devices, controlled conditions such as relative humidity between 50% to 70%, ambient air temperature between 20 °C to 30 °C, and an average refrigerant temperature between −20 °C to −10 °C are changed. The results include frost thickness, density, and heat transfer consequences under various ambient temperature conditions, average refrigerant temperature, and humidity. Based on empirical measurements, the frost accumulated on top of the fin is higher than the bottom, and frost is formed only on the fins' edge and blocks the flow path and short space between the fins. The computational fluid dynamics method is applied to predict the flow field and frost growth on the fins. Comparison between numerical results and experimental data shows that the current numerical method can be utilized more effectively to find out the frost behavior. According to the measurements, correlations are presented for frost growth.