why there are white lime trangle lines on walls aroud my chimney?

Thank you for your explaination. I have checked the thermal insulation in attic are dry and has no water mark. The roof boards are dry. But, because the slope of the roof, the bottom of the roof is hard to reach and also filled with thermal insulation material. I did not check it and I will try now based on your suggestion.

 

When you do get in there for this inspection, take a close look at the chimey while you are there. You may want to use a peice of plywood to slide out there.

 

Thanks for suggestion. What is the reason to slide out a peice of plywood and what should I look for?

 

The plywood just gives you something to lay on while you do your inspection. You are looking for wet insulation. Insulation that looks like it might have been wet. Look at the lumber for signs of water. Check around the chimney and while you are there check that air can get thru from the soffet vents. If in doubt take photos.
I am thinking that you may have had an ice dam in the winter and water worked its way in and drained between the wall and the brick.