Abstract: With the increase of photovoltaic power generation projects, more and more industrial plants have been equipped with photovoltaic panels on the roofs. With the increase of service loads on roof, purlins can not meet the requirements of bearing capacity, so it is often necessary to be reinforced. Combined with the background of a 5 MW self-consumption distributed photovoltaic power generation project, a new method for purlin reinforcement was proposed based on the reinforcement method of enlargement sections, that was, L-shaped angle steel was added at the lower flange of the original C-section purlins for reinforcement, and the two were connected by core-pulling rivets. On that basis, the bearing capacity tests of three reinforced steel purlin specimens were conducted to study the mechanical properties and failure modes of purlins, and the load-displacement curve, load-strain curve, bearing capacity, and stiffness of specimens were obtained. Through the finite element software ABAQUS, the accurate finite element models of specimens were constructed, and the numerical simulation analysis was conducted. The finite element results and test results were compared and analyzed to verify the accuracy of test results and the effectiveness of the new reinforcement method. The results showed that: the new reinforcement method of C-section steel purlins proposed in the paper was feasible. The bearing capacity and stiffness of the reinforced steel purlins could satisfy the requirements of relevant specifications, and the ultimate bearing capacity was about 1.49 times of the design value of bearing capacity of original purlins.