This is filter circuit for fly back transformer,
Back emf is generating in transformer primary when switching heaping, this back emf is dangerous to switching devices and other circuit. so it should suppressed. Diode will conduct during fly-back action and TVS will suppress the excess voltage
It's a kind of 'snubber' circuit although more accurately a voltage clamp. As smijesh points out, when the TNY267 output transistor turns off, it produces a fast high voltage spike at the transformer. The idea is that the normal diode conducts it to the TVS which conducts at it's rated voltage and clamps the voltage from becoming too high. The TVS clamps at about 200V and the FR106 is an 800V fast switching diode.