Why do some units stand guard at the gate of the People's Liberation Army and some units stand guard at the gate of the Armed Police?

The troops of China People's Liberation Army standing guard basically belong to the organs, barracks and combat readiness facilities in the sequence of China People's Liberation Army.

Security tasks of armed police standing guard:

Article 7 of the Law of People's Republic of China (PRC) People's Armed Police stipulates that the People's Armed Police Force shall perform the following security tasks: (1) Armed guards for security targets and major events stipulated by the state; (2) Armed guards of important public facilities, enterprises, warehouses, water sources, water conservancy projects, power facilities and communication hubs related to the national economy and people's livelihood; (3) Armed guarding of bridges and tunnels of important traffic trunk lines; (4) Armed guards outside prisons and detention centers; (5) Armed patrols in key areas and special periods of cities where the people's governments of municipalities directly under the Central Government, provinces and autonomous regions are located and other important cities; (six) to assist the public security organs, state security organs, judicial administrative organs, procuratorial organs and judicial organs in carrying out the tasks of arrest, pursuit and escort according to law, and to assist other relevant organs in carrying out important escort tasks; (seven) to participate in the handling of riots, riots, serious violent crimes, terrorist attacks and other social security incidents; (eight) other security tasks entrusted by the state.