Add timing

Is there any occasion that If we add a lot of timing and no knock appears but some degrees back the power and torque are plateau but we keep add timing, what could happen then?

If the engine is not knock limited due to a high octane fuel then yes, we can get a situation where we can add timing beyond MBT. The result generally will be less torque and power. You're also adding more cylinder pressure earlier in the engine cycle while the piston is still coming up to TDC. There's no advantage of course in advancing the timing beyond MBT.