Grain number per spike is a key determinant of the yield of cereal crops and this trait is largely controlled by the inflorescence structure. Over the last several decades, wheat breeders have increased grain yields mainly by increasing the number of grains produced in each inflorescence in common wheat (Triticum aestivum L.). In common wheat, grain number per spike can be dissected into two important traits, the number of spikelets per spike and the number of fertile florets per spikelet, of which the underlying genetic bases remain largely unknown. Here, we identified and characterized the SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) proteins in wheat, which plays vital roles in plant growth and development, affecting plant architecture, panicle structure, organ size and grain number. In the present study, 56 TaSPL genes were identified in the wheat genome and divided into eight phylogenetic groups (namely G1-G8). Moreover, qRT-PCR-based expression analyses of TaSPL genes in several wheat tissues, together with the publicly available RNA-seq data, revealed distinct spatial-temporal expression patterns of the TaSPL genes. According to the expression profiles, TaSPL13 is highly expressed in the spike, indicating its involvement in spike development. Therefore, TaSPL13 genes were cloned and TaSPL13-2B was selected to generate transgenic plants of wheat using the wheat cultivar Bobwhite. Compared with the wild type, the transgenic lines had significantly increased number of florets and grains per spike, suggesting that TaSPL13-2B regulates spikelet development in wheat. The research work reported here laid the foundation for unveiling the functions of TaSPLs in the spike development of wheat and provides useful candidate genes for yield improvement.