The dual and triple modular redundancy concept and implementation principle in HVDC control and protection system are presented in detail. The protections whose single component fault may lead to HVDC blocked are listed. For the circumstances that the protection is dual modular redundancy， but the sensor is singly configured， the solutions of ABB and NARI in order to prevent failures caused by single component fault are compared. Three outage accidents caused by measuring device or sensor not fully dual modular redundancy are analyzed. The problems and solutions of triple modular redundancy in protection system of Gaoling converter station are introduced. The disposal advice is given to the existing deficiencies about dual modular redundancy in current HVDC projects. When a system is in maintenance， abnormalities of the other system may lead to HVDC outage. A recommended fundamental solution is the signal contacts， control and protection are all triple modular redundancy. When using the“three take two” logic protection， the equipments with three or more channels should be chosen to avoid HVDC outages caused by the individual component or board failure.