Abstract: The interfacial transition zone ( ITZ) is a weak area in the cement concrete structure． In order to obtain the deterioration behavior of the ITZ suffering the working environment in North China，coupled loading condition of fatigue load， freezethaw cycles and dry-wet was conducted to simulate the working condition of pavement concrete． Digital image processing technology was used to extract and analyze the structure of pavement concrete interface area in different working stages， the dynamic process of the interface structure of the pavement cement concrete under the three fields was revealed，and then microcosmic damage mechanism of pavement cement concrete was studied． Ｒesults show that after three months of standard curing， the width of ITZ of concrete is between 30 ～40 μm; with the increase of the coupling time of load， freezingthawing and dry-wet circulation， the fatigue life of concrete is obviously shortened，and when the fatigue damage is reached， the width of ITZ is close to 60 ～70μm; the expansion rate of ITZ increases obviously，the structural density of the concrete decreases gradually，the maximum crack length extends first and then decreases，and the maximum width of the crack increases gradually; finally， the width of ITZ and the critical value of the structural parameters of ITZ are determined． 

Key words: pavement concrete, load, freezethaw damage, threefields coupling, interfacial transition zone, fatigue damage, damage mechanism