A 3D printing method implemented by movable platform, adopted by a 3D printer having a nozzle and a printing platform, the method comprising: a) calculating respectively a starting point and an ending point of each of a plurality of swaths of a printing layer; b) calculating movement information of the printing platform upon an X axis and a Y axis of the 3D printer according to the starting points and the ending points, wherein the nozzle is fixed at a center of the 3D printer and immovable upon the X axis and the Y axis, and a length of an internal space of the 3D printer is twice to a length of the printing platform; c1) controlling the printing platform to move along the X axis for locating the printing platform and making the nozzle to be at the starting point of one of the plurality of swaths upon the printing platform; c2) controlling the printing platform to move only along the X axis and the nozzle to jet ink for printing the swath while the printing platform moves to corresponding positions, and making the nozzle to be at the ending point of the swath upon the printing platform at the end of the printing action of the swath; c3) if determining that the swath printed in the step c2 is not a final swath of the printing layer, controlling the printing platform to move along the Y axis according to the movement information for locating the printing platform and making the nozzle to be at the starting point of next one of the plurality of swaths; c4) re-executing the step c1 to the step c3 to print the next one of the swaths of the printing layer; and d) re-executing the step c1 to the step c4 before all printing actions for the plurality of swaths of the printing layer are completed. a) calculating respectively a starting point and an ending point of each of a plurality of swaths of a printing layer; b) calculating movement information of the printing platform upon an X axis and a Y axis of the 3D printer according to the starting points and the ending points, wherein the nozzle is fixed at a center of the 3D printer and immovable upon the X axis and the Y axis, and a length of an internal space of the 3D printer is twice to a length of the printing platform; c1) controlling the printing platform to move along the X axis for locating the printing platform and making the nozzle to be at the starting point of one of the plurality of swaths upon the printing platform; c2) controlling the printing platform to move only along the X axis and the nozzle to jet ink for printing the swath while the printing platform moves to corresponding positions, and making the nozzle to be at the ending point of the swath upon the printing platform at the end of the printing action of the swath; c3) if determining that the swath printed in the step c2 is not a final swath of the printing layer, controlling the printing platform to move along the Y axis according to the movement information for locating the printing platform and making the nozzle to be at the starting point of next one of the plurality of swaths; c4) re-executing the step c1 to the step c3 to print the next one of the swaths of the printing layer; and d) re-executing the step c1 to the step c4 before all printing actions for the plurality of swaths of the printing layer are completed.