Spinach (Spinacia oleracea L.) is an important leafy vegetable crop, and its leaf characteristics are important for spinach germplasm innovation and new variety breeding. In this study, spinach inbred lines P₁ and P₂ were used as parents to construct six-generation segregating populations. Based on multi-location trials, we adopted an improved analytical procedure for the major gene plus polygene mixed genetic model, and the genetic models governing leaf length, leaf width and petiole length in spinach were screened. Furthermore, a high-density genetic linkage map of spinach was constructed using re-sequencing data from 152 individuals of the F₂ population, and QTLs (quantitative trait loci) governing spinach leaf type were mapped to identify their candidate genes. The results showed that the optimal genetic model for leaf length was MX1-AD-ADI, for leaf width was MX1-AD-ADI, and for petiole length was MX2-ADI-AD. The genetic map developed from the F₂ segregating population contained 5900 bin markers assigned to six linkage groups, spanning a total genetic distance of 843.48 cM. One QTL associated with leaf length was mapped on chromosome 2 and designated qLL2-1, yet no candidate genes were identified within its candidate interval. Two QTLs controlling leaf width were mapped on chromosome 1 and chromosome 2, designated qLW1-1 and qLW2-1, respectively, and 15 genes were annotated in this candidate region. One QTL related to petiole length was located on chromosome 2 and named qPL2-1, with four genes annotated in its candidate interval. Combined with spinach genome annotation and expression-level analysis of candidate genes, the gene SOV2g023140 was identified as the candidate gene regulating spinach leaf width, which was named SpPINL2. Meanwhile, three genes regulating petiole length constituted a gene cluster FAR1-ULP-zf-GRF, designated SpFAR1-ULP-zf-GRF.