A design of radiation hardening Low Dropout Regulators(LDO) is presented, which consists of high precision reference,error amplifier,power transistor and power reset time controlling circuit,and so on. The estimation method of the device parameters variation is introduced in detail in total ionizing dose and neutron radiation experiment by simulation. The chip is fabricated in 0.6 μm BiCMOS technology. The results indicate that the product not only meets application requirements but also performs well in radiation hardening when the total ionizing dose attains to 3×103 Gy(Si) and neutron fluence attains to 0.6×1014 n?cm-2. It is applicable to nuclear radiation environment and the test results prove the correctness of the design.