In the present paper, a class of non-weight modules over the super-BMS 3 algebras S ǫ (ǫ = 0 or 1 2 ) are constructed. These modules when regarded as S 0 -modules and further restricted as modules over the Cartan subalgebra h are free of rank 1, while when regarded as S 1 2 -modules and further restricted as modules over the Cartan subalgebra H are free of rank 2. We determine the necessary and sufficient conditions for these modules being simple, as well as determining the necessary and sufficient conditions for two S ǫ -modules being isomorphic. At last, we present that these modules constitute a complete classification of free U (h)-modules of rank 1 over S 0 , and also constitute a complete classification of free U (H)-modules of rank 2 over S 1 2 .