For an enclosure even cardboard will work.

I calibrated my new Solidoodle, and try a couple of tiny print, they been well. But when I tryed to print a biggest part, at the end when I lift it up, it crack in the middle. I also noticed that the nozzle temperature fell to 190 from 200 degrees during printing.
Give me a clue to fix that

The cracking is caused by the cooling down of the part: if it happens too fast, the binding force between the layers is not enough to compensate for the strain caused by the thermal shrinking. Is your printer located in a cold environment?

The solution is:

1) Get en enclosure
2) Run a PID calibration (http://www.soliwiki.com/PID_tuning)
3) Let the parts cool down inside the printer.

(or: switch to PLA that does not shrink that much while cooling down)

and 4) try to get rid of any banding issues... I cannot see from your picture but they are fairly common.

If you don't have an enclosure handy, in the meantime try just running a PID calibration and hopefully that will help keep your extrusion temperature constant.