2个说法都对,但是用法不一样. two meters long 可以做表语或者后置定语,如：The bridge is two meters long.（表语） 或者 It is a bridge two meters long.(后置定语) two- meter -long 是一个词--合成词,只能作前置定语,如：It is a two- meter -long bridge.
记得采纳啊