Disclosed is a deep heavy oil steam-injecting string for a combined insulation tubing in a directional well. The upper segment of a directional sleeve is a vertical segment, and the lower segment of the directional sleeve is a directional oblique segment. The upper end of the directional sleeve is connected with a well mouth device. A thermosensitive packer, a compensator, a lower segment of an insulation oil tube, a variable-diameter supporting connector and an upper segment of the insulation oil tube are sequentially connected from the bottom up and then enter downwards into the directional sleeve. The upper end of the upper segment of the insulation oil tube suspends on the well mouth device. Size of the upper segment of the insulation oil tube is larger than that of the lower segment of the insulation oil tube. The variable-diameter supporting connector is arranged on the directional oblique segment of the directional sleeve and supports on the directional sleeve. The lower segment of the insulation oil tube is light. Working stress of the upper segment of the insulation oil tube is low on a connecting position of the well mouth device. The lower segment of the insulation oil tube is supported on the directional sleeve by the variable-diameter connector, so that the working stress of the upper segment of the insulation oil tube is lowered on the connecting position of the well mouth device, length of the insulation oil tube is increased to 2000m or above, full wellbore insulation steam injection of the deep directional heavy oil well is achieved, and steam injection effect of the deep directional heavy oil well with depth over 2000m is improved.