By their unique and excellent optical properties, femtosecond lasers have brought novel developments and methodologies in biophotonics researches. In researches of cell and molecular biology, femtosecond lasers can perform precise stimulations and operations to cells at the subcellular or diffraction limit level. In this article, calcium signal modulation in human cells by femtosecond lasers is reviewed, possible mechanism of optical release of cellular calcium store is discussed, and physical and physiological processes of the release are analyzed. The hypothesis of cellular responses to femtosecond lasers is investigated at cellular and molecular level, with demonstrations of following molecular and physiological processes. This all-optical modulation of molecular signals is very important to the researches of cellular signaling pathways, which can be further applied in optical regulation of gene expression and stem-cell differentiation.