Fluorescent carbon dots (CDs) are drawing increasing attention due to their excellent properties, however, CDs usually show excitation-dependent emission property. Herein, we prepared a series of multi-excitation and single color emission carbon dots doped with nitrogen and silicon (SiN-CDs) by one-pot hydrothermal method from a hyperbranched polysiloxane. Interestingly, the synthesized SiN-CDs have three excitation bands at around 240, 300 and 360 nm, and only one emission band at around 440 nm. Meanwhile, SiN-CDs emit single color light in a wide excitation range and different concentrations. Structural and optical property characterizations show that the multi-excitation and single color emission property of SiN-CDs is caused by the cooperation of the sp(2) carbon core with the abundant fluorescent groups on the surface. In particular, SiN-CDs have multiple functions, not only can be internalized into live cells with obvious accumulation in cell nuclei, but also possess high selectivity, sensitivity and anti-interference ability in detecting of Fe3+.