The present invention relates to an apparatus and a method for monitoring a hydrate decomposition area under different drilling and production processes. The apparatus for monitoring hydrate decomposition area under different drilling and production processes comprises a reaction unit, an auxiliary unit and a determination unit; the reaction unit is used to simulate the hydrate storage layer environment, provide a place for generation and decomposition of a hydrate, simulate a hydrate heat-injection exploitation process, a hydrate pressure-reduction exploitation process and a hydrate CO2 displacement exploitation process, and also analyze the hydrate decomposition status at various areas by calculating the hydrate decomposition rate, thereby evaluating and optimizing the drilling and production process; the auxiliary unit is used to provide a gas source and a liquid source for the reaction unit, and simulate different hydrate drilling and production processes; and the determination unit is used to measure the hydrate decomposition rate in different drilling and production processes.