The invention discloses a UHVDC transmission control method and control device based on a calculation voltage value. A midpoint voltage measurement fault is determined according to a 12-12 pulsating DC pole midpoint voltage measurement value or a midpoint voltage measurement point feedback signal, and a valve group voltage calculation value is employed as a feedback voltage for control; a voltage correction unit is configured at a rectification side, difference of the valve group voltage calculation value and a valve group voltage reference value is superposed to difference of a valve group current measurement value of a current adjusting unit and a valve group current reference value, and a trigger delay angle of a valve group is controlled through a PI adjusting device according to the result; a voltage control unit is configured at an inversion side, the trigger delay angle of the valve group is controlled through the PI adjusting device according to the difference of the valve group voltage reference value and the valve group voltage calculation value. The method is advantaged in that stable voltage control on UHVDC can be realized without a 12-12 pulsating DC pole midpoint voltage measurement point or under a voltage measurement point fault. The invention further discloses a UHVDC transmission control device based on the calculation voltage value.