Inflorescence type is one of the important ornamental traits of Hydrangea macrophylla. To locate the key genes controlling inflorescence types, 125 H. macrophylla individual plants were re-sequenced to obtain the single nucleotide polymorphisms (SNPs）. Genome-wide association studies (GWAS) based on SNPs and inflorescence types were carried out using general linear model (GLM) and mixed linear model (MLM) of Fastlmm and GEMMA software in order to identify the SNPs strongly associated with inflorescence types. The results showed that, among the 125 Hydrangea plants, 71 had lacecap inflorescences, and 54 with mophead inflorescences. 369 loci were found significantly associating with floral phenotypes （-log10(P)>9）, of which 285 loci were obtained by both GLM and MLM models and explained phenotypic variation from 11.80% to 60.54%. Sequencing and kompetitive allele-specific PCR (KASP) were utilized for further genotyping verification in 34 GWAS populations, 52 hydrangea cultivars, and 7 hybrid populations. A total of 12 SNP loci were chosen from 285 loci. The genotyping results indicated that the four SNPs of Hma1.2p1_0060F.1_796640, Hma1.2p1_0060F.1_1540773, Hma1.2p1_0653F.1_868484 and Hma1.2p1_0669F.1_949341 were closely related to inflorescence type. The genes controlling hydrangea inflorescence type probably locate in three Scaffolds: Hma1.2p1_0060F.1, Hma1.2p1_0653F.1 and Hma1.2p1_0669F.1. To locate the upstream and downstream genes, the 285 SNPs were chosen as the focal point. A total of 1287 genes were annotated, with 1114 and 173 of them having functional annotations and unknown function, respecitively. The gene functions were involved in processes such as DNA replication, signal transduction mechanism, lipid and amino acid transport and metabolism and substance transport. Four candidate genes encoding for transcription factors, namely, two MYBs, one MADS, and one bHLH, were predicted to be associated with hydrangea flowering type. The transcription factors may play important roles in the regulation of flowering organs development in H.macrophylla. The findings provide a theoretical foundation for future gene cloning and molecular marker-assisted breeding.