How to calculate the maximum power of a current mode PWM controller?
In datasheets of Current Mode PWM Controller maximum power at that it
can be operated is not mentioned

You can make a maximum estimate of how much maximum power you can dissipate: -

So, at an ambient temperature of (say) 25 °C, you can allow the package to warm by another 125 °C before the &quot;junction&quot; exceeds its limit. Given that the device has a thermal resistance from internal junction to air of 180 °C per watt, the maximum power that should be dissipated in the device is 0.69 watts.
If you don't have reasonable control over the local ambient temperature around the chip (air flow etc.), it may warm the local ambient another 30 °C so maybe you should aim to dissipate no more than 0.5 watts. But, to be on the safe side I would aim for no more than 0.3 watts.
If you look a little higher up in the table above it also tells you that the maximum voltage is 28 volts and you should not allow more than 20 mA into pin 7 (Vcc). It should say pin 8 by the way; pin 7 is a typo in this data sheet.
So that implies a maximum power limit of 0.56 watts but, I'd try and run at much lower values here because it leaves very little power to activate the MOSFET you need to attach.