A method for vertically positioning an examinee that is horizontally placed on an examination table of a CT device, wherein a sensor for measuring a vertical distance to the examinee is attached to the CT device, and the method comprises: obtaining an initial position of the examination table of the CT device when horizontal placement of the examinee is completed; obtaining a measurement range of the sensor that is corresponding to a to-be-examined organ of the examinee, wherein the measurement range is on the examination table and comprises a start point and an end point in the horizontal direction, wherein the obtaining of the measurement range comprises: obtaining a top-view image of the examinee from a camera; determining an image range corresponding to the to-be-examined organ from the top-view image, wherein the image range is defined by pixel start coordinates and pixel end coordinates in the horizontal direction; mapping the pixel start coordinates to an initial position of the start point of the examination table based on an imaging parameter of the camera and the initial position of the examination table, and mapping the pixel end coordinates to an initial position of the end point of the examination table; determining the measurement range from the start point and the end point; during movement of the examination table toward a scanner gantry of the CT device, when the start point reaches a measurement position of the sensor, causing the sensor to start measuring the vertical distance to the examinee, and when the end point reaches the measurement position, stopping measurement of the sensor, and obtaining a real-time height of the examination table corresponding to each point in the measurement range while the sensor performs measurement; calculating an organ center height based on a plurality of measurement results by the sensor of the distance to the examinee, the height of the sensor, and the real-time height of the examination table corresponding to each point in the measurement range, wherein the organ center height represents an average height within the measurement range of the center of the to-be-examined organ in the vertical direction; and adjusting the height of the examination table based on the calculated organ center height, so that the adjusted organ center height is equal to the isocenter height of the scanner gantry. obtaining an initial position of the examination table of the CT device when horizontal placement of the examinee is completed; obtaining a measurement range of the sensor that is corresponding to a to-be-examined organ of the examinee, wherein the measurement range is on the examination table and comprises a start point and an end point in the horizontal direction, wherein the obtaining of the measurement range comprises: obtaining a top-view image of the examinee from a camera; determining an image range corresponding to the to-be-examined organ from the top-view image, wherein the image range is defined by pixel start coordinates and pixel end coordinates in the horizontal direction; mapping the pixel start coordinates to an initial position of the start point of the examination table based on an imaging parameter of the camera and the initial position of the examination table, and mapping the pixel end coordinates to an initial position of the end point of the examination table; determining the measurement range from the start point and the end point; obtaining a top-view image of the examinee from a camera; determining an image range corresponding to the to-be-examined organ from the top-view image, wherein the image range is defined by pixel start coordinates and pixel end coordinates in the horizontal direction; mapping the pixel start coordinates to an initial position of the start point of the examination table based on an imaging parameter of the camera and the initial position of the examination table, and mapping the pixel end coordinates to an initial position of the end point of the examination table; determining the measurement range from the start point and the end point; during movement of the examination table toward a scanner gantry of the CT device, when the start point reaches a measurement position of the sensor, causing the sensor to start measuring the vertical distance to the examinee, and when the end point reaches the measurement position, stopping measurement of the sensor, and obtaining a real-time height of the examination table corresponding to each point in the measurement range while the sensor performs measurement; calculating an organ center height based on a plurality of measurement results by the sensor of the distance to the examinee, the height of the sensor, and the real-time height of the examination table corresponding to each point in the measurement range, wherein the organ center height represents an average height within the measurement range of the center of the to-be-examined organ in the vertical direction; and adjusting the height of the examination table based on the calculated organ center height, so that the adjusted organ center height is equal to the isocenter height of the scanner gantry.