Often designer needs require making openings in concrete slabs to provide extra service .Therefore it was necessary to study the size and the location of the opening in the slab and show the effect of it in the behavior of the slab. The aim of this study was to carry out nonlinear finite element analyses modeling of concrete slabs reinforced by CFRP bars and determine the effect of size openings on the structural behavior of the flat slabs in consideration, by using the ANSYS 19 program. All models were 3 by 3 panels of square flat slabs; each of them had dimensions 4000 x 4000 mm with a marginal beam and reinforced by carbon fiber polymer bars. At first, the dimension of the opening is studied by taking 2000 x 2000mm, 1000 x 1000mm and 800 x 800mm in the field strip. The second case of study was the location of the opening in different position of the slab to choose the best location of it. The flat slab was analyzed without openings and with different size openings for comparison. Finite element verification was made by comparing experimentally tested CFRP concrete slab with central opening with numerically solved specimen and showed good agreement. Results indicated that slabs with openings in the field strips possess better stiffness. The ultimate loads for slabs with central opening at the central panel decreased to around 14% of that without opening .In case of central opening at corner panel, the ultimate loads revealed higher reductions in ultimate load that reached 33% of that of the slab without opening