In order to study the relationship between strains and corrosion levels of prestressed concrete beams uder fatigue loading, accelerated corrosion method is used to make various corrosion rates of prestressed steel strands. The beams have the same designs and submitted to the same maximum and minimum load during the test. With the corrosion level as main parameter, strains at different position of the beams, such as non-prestressed steel strain, concrete strain in compressive region at mid-span and prestressed steel strain are studied. The test results show that beams with different corrosion rates have the same “three-stage“ law on the development of non-prestressed steel maximum and residual strain,as well as concrete strain and prestress strain. The significant increase of concrete strain is generated due to corrosion after concrete cracking.The increase of non-prestressed steel strain is nearly proportional to the growth of corrosion under the same fatigue load. A relationship was found to be a function. It can be obtained the corrosion rate of prestressed steel when the stress of non-prestressed steel strains are measured.