A coupler mounting assembly for rail vehicles, comprising a coupler box body for placing a coupler, wherein the coupler mounting assembly further comprises a mounting seat provided on two sides of the coupler box body; a stop seat fixed on two sides of the coupler box body and extending along a length direction of the coupler box body, wherein the stop seat is located at a front end of the mounting seat; a coupler body support plate mounted to the mounting seat and abutting against the stop seat to limit movement of the coupler toward a forward direction of the rail vehicle; a position-limiting block fixed on two sides of the coupler box body and extending along the length direction of the coupler box body, wherein the position-limiting block is located at a rear end of the mounting seat; and a stop block which is slidably connected with the position-limiting block and abuts against the coupler body support plate, wherein the stop block is movable within a certain range relative to the position-limiting block along the length direction of the coupler box body, and the stop block and the stop seat are respectively located at a rear end and a front end of the coupler body support plate, the coupler mounting assembly is characterized in that, the position-limiting block comprises a vertical plate provided along the length direction of the coupler box body; a locking end provided on an upper surface of the vertical plate, located at a rear end of the position-limiting block and extending upward; a notch provided on a front side wall of the vertical plate and extending downward; and mounting holes provided on the upper surface of the vertical plate and located between the locking end and the notch; the stop block comprises a horizontal plate located above the vertical plate and provided along the length direction of the coupler box body, wherein the horizontal plate is longer than the vertical plate; an end face provided on a side wall of a rear end of the horizontal plate for abutting against the locking end; a bent end provided at a front end of the horizontal plate and extending downward to abut against the notch; and via holes penetrating through upper and lower surfaces of the horizontal plate for connecting the position-limiting block with the stop block by mounting bolts, wherein a hole diameter of each via hole is larger than a hole diameter of each mounting hole, and the stop block is movable within a certain range relative to the position-limiting block. a mounting seat provided on two sides of the coupler box body; a stop seat fixed on two sides of the coupler box body and extending along a length direction of the coupler box body, wherein the stop seat is located at a front end of the mounting seat; a coupler body support plate mounted to the mounting seat and abutting against the stop seat to limit movement of the coupler toward a forward direction of the rail vehicle; a position-limiting block fixed on two sides of the coupler box body and extending along the length direction of the coupler box body, wherein the position-limiting block is located at a rear end of the mounting seat; and a stop block which is slidably connected with the position-limiting block and abuts against the coupler body support plate, wherein the stop block is movable within a certain range relative to the position-limiting block along the length direction of the coupler box body, and the stop block and the stop seat are respectively located at a rear end and a front end of the coupler body support plate, the coupler mounting assembly is characterized in that, the position-limiting block comprises a vertical plate provided along the length direction of the coupler box body; a locking end provided on an upper surface of the vertical plate, located at a rear end of the position-limiting block and extending upward; a notch provided on a front side wall of the vertical plate and extending downward; and mounting holes provided on the upper surface of the vertical plate and located between the locking end and the notch; the stop block comprises a horizontal plate located above the vertical plate and provided along the length direction of the coupler box body, wherein the horizontal plate is longer than the vertical plate; an end face provided on a side wall of a rear end of the horizontal plate for abutting against the locking end; a bent end provided at a front end of the horizontal plate and extending downward to abut against the notch; and via holes penetrating through upper and lower surfaces of the horizontal plate for connecting the position-limiting block with the stop block by mounting bolts, wherein a hole diameter of each via hole is larger than a hole diameter of each mounting hole, and the stop block is movable within a certain range relative to the position-limiting block.