Conotruncal heart defects (CTDs) represent a group of severe and complicated congenital cardiovascular malformations and require opportune clinical interventions once diagnosed. Occurrence of CTD is related to the functional abnormality of the second heart field (SHF), and variants of genes which regulate the development of the second heart field have been recognized as the main genetic factors leading to CTDs. Previous studies indicated that transcriptional complex SIX1/EYA1 may contribute to SHF development, and SIX1/EYA1 knockout mice exhibited a series of conotruncal malformations. Here, we recruited and sequenced 600 Chinese conotruncal heart defect patients and 300 controls. We screened out one novel SIX1 mutation (SIX1-K134R) and four EYA1 rare mutations (EYA1-A227T, EYA1-R296H, EYA1-Q397R, EYA1-G426S), all variants were present only in the case cohort, and the mutated sites were highly conserved. We then analyzed mutations by software including Sift, PolyPhen-2, PROVEAN, Mutation Taster, HOPE, and SWISS-PdbViewer. The results showed that the mutations had varying degrees of pathogenic risk, protein properties, spatial conformations, and domain functions which might be altered or influenced. Through biological and in silico analyses, our study suggests an association between SIX1/EYA1 mutations and cardiovascular malformations, SIX1/EYA1 mutations might be partially responsible for CTDs.