The invention relates to a natural gas pressure difference energy recovery and electrolytic hydrogen production integrated system. The natural gas pressure difference energy recovery and electrolytic hydrogen production integrated system is arranged between a high-pressure natural gas trunk line and a low-pressure natural gas trunk line and comprises a natural gas pressure difference energy recovery device, a power generation device and an electrolyzing water hydrogen production device which are connected in sequence. Accordingly, firstly, normal-temperature high-pressure natural gas is subjected to preheating and expansion depressurization through a first preheating device and an expander unite of the in sequence natural gas pressure difference energy recovery device to form normal-temperature low-pressure natural gas; then, the mechanical work output by the expander unit is converted into power energy through the power generation device; and finally, the power energy output by the power generation device is used for electrolyzing water to produce high-purity hydrogen through the electrolyzing water hydrogen production device; sufficient natural gas pressure difference energy recovery can be achieved, and then pressure difference energy is converted into the power energy used for electrolyzing the water to prepare the high-purity hydrogen of which the purity reaches up to 99.99%; meanwhile, the low-pressure natural gas is also prepared in a pipe network.