The invention discloses a method to acquire human body safety envelopes, comprising the steps of using the width direction of a bed body as an x axis, the length direction of the bed body as a y axisand the height direction of the bed body as a z axis to establish an xyz right-angled coordinate system; making a high slope shot for a human body lying flat on the bed body through a first camera from above, and screening high-slope outlines DP of the human body to obtain X coordinates and Y coordinates of human body outlines HP; calculating a human body center line L1 according to an average oftwo values x1 corresponding to each y1 in the high-slope outline; photographing a lateral projection of the human body, formed on a background board, through a second camera in a horizontal directionperpendicular to the human body center line L1, and screening to obtain human body side outlines SP; acquiring Z coordinates of the human body outlines HP according to z2 and the human body center line L1 so as to obtain the human body outline HP. The method has the advantages of high efficiency, low cost, good implementing simplicity and high stability.