The invention relates to a pyroelectric energy balance measuring device and an energy measuring method, in particular to a multichannel pyroelectric energy balance measuring system and an energy calculation method. The energy balance measuring system comprises a pyroelectric detector, a single-ended-to-differential converter, a front programmable gain amplifier, a back programmable gain amplifier, a band-pass filter, a main channel amplifier, a redundant channel amplifier, a signal acquisition and control module and a gain and band-pass filter bandwidth control module, wherein the signal acquisition and control module analyzes and processes acquired signals by a self-adaptive spectrum analysis method and transmits a result to the gain and band-pass filter bandwidth control module; and the gain and band-pass filter bandwidth control module loads the result to the front programmable gain amplifier, the back programmable gain amplifier and the band-pass filter. By adoption of the system and the method, gains of the amplifiers and the bandwidth of the band-pass filter can be conveniently adjusted on line.