A light source for extreme ultraviolet (EUV) radiation is provided. The light source includes a target droplet generator, a laser generator, a measuring device, and a controller. The target droplet generator is configured to provide a plurality of target droplets to a source vessel. The laser generator is configured to provide a plurality of first laser pulses according to a control signal to irradiate the target droplets in the source vessel, so as to generate plasma as the EUV radiation. The measuring device is configured to measure process parameters including temperature of the source vessel, droplet positions of the target droplets, and beam sizes and focal points of the first laser pulses. The controller is configured to provide the control signal according to at least two of the process parameters.