Abstract: Subthreshold micropulse laser photocoagulation(SMLP) is an alternative to the conventional continuous-wave laser for the treatment of diabetic macular edema (DME). In contrast to the conventional laser, the therapeutic effect of the SMLP is not accompanied by thermal retinal damage. In SMLP, a train of repetitive short laser pulses delivers the laser energy within an “envelope”, which was described as“duty cycle”. Each “envelope” includes “ON” time, which is the duration of each micropulse, and “OFF” time, which is the time between the micropulses. The “OFF” time is important since here the originated heat can cool down. This leads to the required activation of the RPE cells, promotes rapid absorption of subretinal and intraretinal edema, but the thermal wave will only reach the neural retina at temperatures beneath the protein denaturation threshold. As a low-energy, high-density laser photocoagulation mode, SMLP is expected to be the first choice for the treatment of DME. It has been proved that SMLP alone or in combination with other therapies, achieved better visual outcome and edema regression, without any thermal damage to the retinal neurosensory layer and choroid. In this article we will review the mechanism, development history and applications of SMLP for DME.(Int Rev Ophthalmol, 2019, 43: 170-175)