We present a thermal gradient convective polymerase chain reaction (PCR) for parallel DNA amplification with different annealing temperatures. The thermal gradient for microfluidic gradient PCR is produced by an innovative fin design whose formation principle is given. Without the need for a pump, the buoyancy forces continuously circulate reagents in a closed loop through different thermal zones, which brings self-actuated convective-flow PCR. In our prototype, we measured a temperature difference of about 45℃ along the gradient direction on the copper flake (45×40×4mm). When the temperature of the hot zone is 90-97℃ and the temperature of the cold zone is 60-70℃, the convection triggered two-temperature amplification of 112-bp fragment of Escherichia coli DNA. The time for amplification is less than 45 min. Interestingly, parallel DNA amplification with different annealing temperatures ranging from 60 t0 70℃ was performed by this method. The PCR thermocycler demonstrated herein can be further scaled down and the loop Iength can be further reduced, and therefore the PCR times can be further reduced. These devices are suited as a platform for a new generation of low-power, portable DNA analysis systems.