Can I Find Out Temp Through Basic MUC 8051?

Of course. Very common. It will be easier or harder depending on which 8051 you get.

I suggest spending a good deal of time reading 8051 datasheets. They may even have an application note that shows how to do just what you want.

fine,,... thanks

If you need to grab an analog signal from a temperature sensor, then process, trigger an alarm, and/or display that signal, you might find it easier to use another microcontroller that has built-in AtoD capability.

For simple tasks, low cost, free dev-tools, and easy serial in-circuit programming, I prefer to use certain parts from Microchip. This little example PIC12F615 has up to 4 AtoD inputs and might fit your application better. There are many other microprocessor manufacturers and you should evaluate which one best fits all your design criteria.