I have installed 10KW X3-Hybrid-G4 inverter with 20kw solar panels, but the AC output power always no more than 10kw, what should I do?

It is normal, this type of iniverter support 200% DC oversizing, it means can let the inverter start generating power at an earlier time and ending at a later time to increase PV generation, but it will not affect the inverter rated output power, what's more, part of the oversizing DC power can be charged to battery as well.