A real-time exposure dose control algorithm for DUV excimer lasers in a step and scan projection lithography is presented. By establishing an abstract scan exposure model and analyzing the pulse to pulse energy fluctuation characteristics of DUV excimer lasers, a real-time dose regulation is implemented based on closed loop feed back control, which especially focuses on reducing the pulse energy overshot and the pulse to pulse stochastic fluctuation. The experiment conducted on an ArF excimer laser with 193 nm of wavelength, 4 kHz of repetition rate, and 5 mJ of pulse energy confirms that such a real-time dose control algorithm is able to achieve a dose accuracy of above 0.89% even with only 20 pulses. It is fully expected that this algorithm will not only meet the more and more stringent dose accuracy requirement for sub-half-micron lithography, but also be helpful to improve the lithography throughput as well as the efficiency.