In order to solve the problems of reduced air flow area，increased heat transfer resistance，and higher refrigerator energy consumption caused by frosting on the evaporator surface，a frosting test platform for evaporators with vertical air ducts was built，and an experimental study was conducted on the distribution characteristics of the frost layer on the evaporator surface along the air flow direction.The frost layer thickness at different times was measured in zones using a timed imaging device，and the average density and average thermal conductivity of the frost layer on the evaporator surface were calculated.The experimental results show that when the inlet coolant temperature is decreased from -15 ℃ to -20 ℃，the difference in blockage rate between Zone 4 and Zone 5 is only 8%，and a lower cold surface temperature is beneficial to the uniform distribution of the frost layer.When the relative humidity increases from 75% to 85%，the average blockage rate increases by 9.4%~55.7%.An increase in relative humidity significantly promotes the growth of the frost layer.Based on the three stages of flat‑plate frosting，the changes in thermal conductivity and frost layer density over time are divided into three stages：rapid growth period，uniform growth period，and stable period.In the late frosting period，the average density is concentrated in the range of 250~300 kg/m³，and the average thermal conductivity is in the range of 0.25~0.30 W/（m·K），with an overall trend of first increasing and then stabilizing.The research conclusions can provide theoretical support for the optimal design of heat exchangers in air‑cooled refrigerators.