In the photovoltaic (PV) full DC collection and transmission system, a short circuit fault on the high voltage DC (HVDC) side will lead to a decrease in power absorption capacity of the high voltage side DC grid. PVs cannot detect the fault of the high voltage side DC grid in time, therefore its output power remains unchanged, which results in the system overvoltage and causes the system to shut down. To address this problem, a fault ride through strategy based on the active voltage rise is proposed. While the voltage of the high voltage side submodule of the high voltage DC transformer is risen to a certain level, the number of the medium voltage side submodules which output the high voltage level is increased to rise the voltage of the medium DC bus. And with the maximum power point tracking (MPPT) converters which have the function of fault state P-V droop, the MPPTs enter the power limiting mode in advance to achieve the power balance of the high voltage DC transformer, thus reduces the overvoltage of the submodule capacitor, and achieves the fault ride through function. The overvoltage of the HVDC transformer submodule under the proposed strategy is analyzed, and the effectiveness and necessity of the strategy are verified by simulation.