On the base of recorded data in many years from the network of geomagnetic observation in China, the anomalous feature of appearance time for minimum of diurnal variations (low-point time)of the geomagnetic vertical component and the variation of their spatial distribution (phenomena of low-point displacement)are studied. Such phenomena of geomagnetic anomalies is well-correlated with strong earthquakes. It is found that most earthquakes occur near the boundary line of sudden changed low-point displacement and generally within four days before or after the 27th and 41th day counting from the day of anomaly appearance. The low-point displacement also appearanced on Oct. 10, before west to Kunlun Mountain Pass M_S 8.1 earthquake on Nov. 14, 2001. The possible "induced magnetic effect trigger" mechanism of the low-point displacement is studied.