A method using modulated continuous wave (CW) visible laser to measure time-resolved fluorescence spectra of trivalent rare-earth ions has been developed. Electro-optic modulator was used to modulate the CW pumping laser with a rise time of 2 μs. CW Nd(3+) lasers were used as examples to present the method. Upconversion dynamic process of Ho(3+) was studied utilizing a 532 nm CW laser. Quantum cutting dynamic process from Tb(3+) to Yb(3+) was analyzed by a 473 nm CW laser. This method can be applied to any CW laser such as He-Ne laser, Ar(+) laser, Kr(+) laser, Ti:sapphire laser, etc.