Natural hazards and disasters in China have increased in magnitude and frequency in recent years as consequences of the fast urbanization promotion and global climate change, which has greatly threatened to the sustainable development of social economy. The widespread devastation, economic damages and loss of human lives, caused by numerous forms of natural emergency situations,' are becoming more serious. The emergency surveying and mapping service system (ESMSS), which is able to make practical contributions to planning and operation of civil protection and disaster reduction, is urgently needed. The paper probes into some key techniques involved in the construction of, the ESMSS at first. Taking applications in "4 ? 20 Lushan earthquake as an example, the -article deeply analyses the problems in data acquisition, transmission, processing, distribution, sharing of the current ESMSSs and their working mechanism. Then, the construction method- of the proposed taskdriven ESMSS is presented in details. Finally, the key techniques including focused service mechanism are expounded.