The invention provides an integrated internal circulation type 
denitrification and 
decarburization bio-
membrane reactor and an operating method thereof. The main body of the reactor consists of an anoxic zone on the lower part, an aerobic zone on the upper part and a 
settling zone on the periphery of the aerobic zone; a composite filler is filled in the anoxic zone, and a water inlet 
pipe is communicated with the bottom of the anoxic zone; the aerobic zone is partitioned into a filler zone for adding a carrier on the upper part and a mud-water 
mixing zone on the lower part by adopting an 
orifice plate, the anoxic zone and the aerobic zone are partitioned through an impermeable partition plate, and a plurality of 
aeration pipes are arranged at the bottom of the aerobic zone and provided with air inlet pores; and the 
settling zone consists of three parts, namely a 
clean water zone, a contact 
settling zone and a 
sludge returning zone which are sequentially arranged from top to bottom, wherein the bottom of the 
sludge returning zone is provided with a 
sludge returning seam and communicated with the bottom of the aerobic zone. The reactor realizes zero 
power consumption in sludge returning, and is compact in structure; and a back flushing 
system is not required in the contact settling zone, and additional agents and carbon sources are not required, so that the reactor is low in running cost.