The tyrosine kinase Src is activated in a large number of human malignancies and plays significant roles in the development of cancers. Activation of Src in human cancers employs a variety of mechanisms mainly including covalent modification, allosteric regulation, gene mutation. Covalent modifications of Src mainly include phosphorylation and oxidization. Tyr530, Tyr419, Thr34, Thr46, Ser72, Tyr138 and Tyr213 are phosphorylation sites of Src, among which Tyr530 and Tyr419 are the most important ones. Allosteric regulations of Src involve its regulatory Src homology 3 (SH3) or SH2 domains，which interacts with allosteric regulators, such as FAK, PR, ER, AR, P130Cas, PDGF, PDGFR, EGFR, HER2, IGF-1R, FGFR-1, c-Met, p13, Nef and Sin. In this review, we summarize the key mechanisms regulating Src kinase activity in cancer cells.