In the present papcr, the measurements and comparisons of a stress field for the ncw and old frame of a tractor arc made by the photoclastic-coating mothod and the moirc mcthod. Somc concrete propositions to change the form of a tractor's frame are put forward, subsiantial cconomic profits can be amassed. It is shown that the two mcihods are admirably applicable to the stress mcasurement of thc thin-walled steel structure.