Is the current generated by the photodiode DC or AC? Why is there an offset after I zoom in?

This circuit was originally designed as an AC amplification test circuit, with AC coupling capacitors at the input and DC blocking capacitors at the output. Therefore, regardless of amplifying DC, pulsating DC, or very slowly changing AC signals, bias will occur.

If you don't want to be biased, short-circuit the input and output capacitors and try it.

Of course, the magnification and feedback capacitance also need to be determined according to the actual situation.

Your circuit can only amplify the AC signal, and the light of the photocell keeps changing before it outputs

It is precisely because of the DC blocking effect of the capacitor that the obtained signal is offset compared with the original signal, that is, it is not at the original level.