Abstract The Tangshan earthquake ( M = 7.8, 28 July 1976) occurred in North China, where there is relatively dense network of geomagnetic observations. Before the earthquake there were anomalies of ∼ 8–10 nT in the total intensity of the geomagnetic field at Ninghe and Dongtietou sites, 50–90 km from the epicenter, and also in the Beijing survey area. Anomalous changes in the vertical component of the geomagnetic field before the earthquake amounted to −12 nT at Tangshan site, and 10 nT at Changli station, which was ∼ 80 km from the epicenter. There were also anomalous short-period geomagnetic variations before and after the earthquake. To investigate tectonomagnetic effects, we measured the magnetic field at 17 sites near an underground nuclear test in 1983 in West China. The total field changed by 2 nT at the time of the explosion, and there were changes of 1–2 nT before and after the explosion. We have also measured the magnetic field around the Miyun reservoir during 1983–1987 and observed a correlation between geomagnetic changes and variations of water level in the reservoir.