In the past decades, micro-seismicity, mainly induced by fluid injection (or depletion), has attracted considerable interest due to its ability to monitor the development of unconventional oil/gas field, such as volumetric extension of hydro-fractures in tight and shale gas fields as well as geo-hazards due to reservoir subsidence. With the deployment of portable (e.g. surface and downhole geophones) and permanent (such as optical fiber) monitor systems, invaluable information of fluid flow path, local stress changes, geomechanical deformation can be inferred from micro-seismic data, though it is still very challenging to interpret the results without any ambiguity. In this paper, we briefly review some key ingredients of micro-seismic data processing, such as data acquisition, characteristics of micro-seismic events, event onset time auto-picking, event location and relocation as well as source mechanism analysis. The uncertainties and issues of current processing workflow are addressed, which is critical to integrate the micro-seismicity into reservoir monitor tool. Finally potential improvement and application are discussed, such as new distributed acoustic system.