Abstract: This paper,basing on the observational data of earth resistivity in more than 20 years on the Chinese continent, analyzes the relation between the precursory anomalous characteristic of earth resistivity and the earthquake's three elements; presents a practical result in which the earthquake strength shpws a linear relation with the logarithm of product of anomaly duration and epicentral distance; studies different kinds of short term and imminent precursory characteristics of seismic earth resistivity and their appli-castion in earthquake prediction, discusses the precursory variation mechanism of earth resistivity.