Abstract: Abstract: In this paper, a method for measuring the transmission attenuation rates of dust accumulation in photovoltaic modules was proposed. The test platform was built independently, and the test system was installed in the roof area without shelter. The system ensured that the total solar irradiance was monitored throughout the day and that the system operated in a naturally dusty state. The test period was selected in May with relatively less rainfall, less sand-dust storm and non-heating period. It can better control test conditions and ensure high test accuracy. In the urban area of Hohhot, the particle size distribution, morphology and element composition of the ash particles were tested and analyzed based on the dust accumulation of glass plates and photovoltaic modules tilted 40.48° to the south. The effects of solar incident angle and the direction of the total solar irradiance on the transmission attenuation of dust accumulation were studied. The daily average transmission attenuation of dust accumulation under different mass of dust accumulation was calculated quantitatively. The results showed that the particle size distribution range of the ash particles of photovoltaic modules was 0.112-199.6 μm, the volume average diameter was 23.10 μm, and the particle size distribution curve was a positively skewed bimodal distribution with long head and short tail. The ash was mainly composed of silt (4 to 63 μm) and the content was about 72.77%. The contribution rates of dust accumulation from large to small were far source substance, regional substance and local substance. Most of the dust accumulation was directly transported and settled to the surface of photovoltaic module through atmospheric circulation. The dust particles of photovoltaic modules were composed of fine quartz crystals or aluminosilicates, most of which were approximately spherical and some of which were amorphous. The main detectable elements of ash particles were crustal elements O, Si, Al, Fe, Ca , Na and Mg. The total attenuation rates of solar irradiance caused by dust accumulation were 1.29% and 3.42%, respectively when the dust accumulations were 2.75 and 4.59 g/m2. During the total solar irradiance increase period, the total attenuation rate changed positively with the linear incidence trend of the solar incident angle, and the average reduction rate was 0.22%/1°. When the total solar irradiance decreased, the total attenuation rate decreased firstly and then increased with the incident angle of the sun in a small range. When the incidence angle of the sun increased to 60°, the total attenuation rate began to increase linearly. The lag peak value of total solar irradiance corresponding to the minimum total attenuation rate was 168 W/m2, and the minimum lag value of solar incidence angle was 25.5°. According to the research results, it could guide the selection of dust removal mode and the forecasting of dust removal cycle of photovoltaic power generation system in Hohhot. In order to prevent dust from sticking and scratching photovoltaic modules, a soft brush body can be selected as the automatic dust removing device for dry dust removal. Dust removal cycle can be set according to the set dust transmission attenuation rates. In the application, the dust transmission attenuation rate test platform can be installed to the unblocked area of the photovoltaic power station, and the dust transmission attenuation rates can be monitored in real time. When the monitored value reaches the set value, the dust removal device is opened and reciprocating dust. The dust removal device is turned off until the monitored value equals the transmission attenuation rates of the dust-covered glass.