I'm trying to read ADPD1080 driver, I can got all of FIFO and the data
registers. But, I down know how to convert the value into Intensity. My goad is Water Turbidity Measurement System
By intensity are you referring to the light sampled by the photodetectors? The ADPD1080 measures the current signal (photocurrent) from the photodiode. Photodiodes generally have different wavelength characteristics but you should be able to get the illuminance (usually measured in lux or lx) from the photocurrent using the characteristics plot in the datasheet.
You can compute the photocurrent from the ADC code using the settings you have for the TIA. For example in TIA ADC mode (bandpass filter and integrator are skipped in this mode), table 29 of the datasheet shows that the TIA ADC resolution using a 25k feedback resistor is 2.92nA/LSB