Sucrose is a non reducing sugar because

It has a glycosidic linkage between  C-1 of $\mathrm{\alpha }$-D-glucopyranose and C-2 of $\mathrm{\beta }$-D-fructofuranose;

The -OH groups of functional group carbon atoms of both glucose(C-1) and fructose(C-2) are invoved in glycosidic linkage;

No free anomeric -OH group;

Both glucose and fructose are in acetal form;

It is a non reducing sugar;