Deviations of stellarator coils during fabrication and assembly are inevitable, which result in error fields. The magnetic configurations in stellarators are dominantly generated by external coils, sensitive to these error fields. Therefore, it is essential to estimate impacts of coil deformations on a stellarator magnetic topology. This paper is dedicated to studying the influence of deformations of nonplanar modular coils (MC) on the magnetic topology in Chinese First Quasi-axisymmetric Stellarator (CFQS). In this work, by changing the Fourier coefficients that represent the CCS and the coil, we obtain two types of deformation coils, i.e., "in-surface" and "out-surface" perturbations on each MC. Subsequently, we utilize three kinds of magnetic islands with rotational transformsι= 2/4, 2/5, and 2/6 to identify coil deviations that have a significant impact on the CFQS magnetic configuration. Serval important results are achieved: (ⅰ) the same deformation of a coil gives rise to various resonant error fields, and the amplitudes of these error fields are different. (ⅱ) The sensitivity of a resonant error field to the deformation of each coil is different. Local deviations of the most complex coil may lead to indistinctive impacts on the magnetic topology. (ⅲ) Resonant error fields are more sensitive to broad perturbations of a coil than local perturbations. These results address that the relaxation of specific coil tolerances is expected to decrease engineering constraints of coil design and fabrication. In addition, this work also helps develop a precise computational model for the forthcoming mapping experiments of magnetic configurations in CFQS.