In 2014, China introduced an ultra-low emissions (ULE) standards policy for renovating coal-fired power-generating units to limit SO₂, NO_x and particulate matter (PM) emissions to 35, 50 and 10 mg m⁻³, respectively. The ULE standard policy had ambitious levels (surpassing those of all other countries) and implementation timeline. We estimate emission reductions associated with the ULE policy by constructing a nationwide, unit-level, hourly-frequency emissions dataset using data from a continuous emissions monitoring systems network covering 96–98% of Chinese thermal power capacity during 2014–2017. We find that between 2014 and 2017 China’s annual power emissions of SO₂, NO_x and PM dropped by 65%, 60% and 72%, respectively. Our estimated emissions using actual monitoring data are 18–92% below other recent estimates. We detail the technologies used to meet the ULE standards and the determinants of compliance, underscoring the importance of ex post evaluation and providing insights for other countries wishing to reduce their power emissions.