The invention relates to a method and a device for identifying a large-sized fracture-cavity type reservoir top enveloping surface of carbonatite. The method comprises the following steps: selecting a first seismic horizon and a second seismic horizon, wherein only a reservoir development section is positioned between the first seismic horizon and the second seismic horizon, and the first seismic horizon, the second seismic horizon and the reservoir development section form a target stratum; determining stratum sections in the target stratum; extracting a crest amplitude or a trough amplitude of each stratum section and time or depth corresponding to each crest amplitude or each trough amplitude; determining a minimum amplitude value of a seismic reflected wave of each stratum section in the target stratum, wherein the minimum amplitude value is a threshold value; comparing the crest amplitude or the trough amplitude corresponding to each seismic channel with the threshold value of the corresponding stratum section to obtain the time or the depth of a reservoir top surface of each seismic channel according to a comparison result; drawing the time or the depth of the reservoir top surface of each seismic channel to obtain the reservoir top enveloping surface in the target stratum.