The invention belongs to the field of technologies for recycling petroleum associated gas in oilfields, and particularly relates to a system and a method for preparing two types of mixed refrigerants by means of recycling LNG (liquefied natural gas)/LPG (liquefied petroleum gas)/NGL (natural gas liquid) products from petroleum associated gas. The system comprises a raw material associated gas pressurization and purification treatment module, an LPG cold box module, an LNG cold box module and a heavy hydrocarbon fractionation module. The raw material associated gas pressurization and purification treatment module, the LPG cold box module and the LNG cold box module are sequentially communicated with an associated gas exhaust device via gas and liquid pipelines, and the heavy hydrocarbon fractionation module is communicated with the LPG cold box module and the LNG cold box module via gas and liquid pipelines. The method includes a process for preparing shallow cooling mixed refrigerants and a process for preparing deep cooling mixed refrigerants. The system and the method have the advantages that series LNG refrigerating technologies implemented by the aid of the two types of mixed refrigerants which are prepared from the products (dry gas, LPG and nitrogen-rich tail gas) in recycling procedures by means of mixing according to specific proportions are utilized, accordingly, shallow cooling and deep cooling purposes can be achieved, the method and the system are simple in procedure, novel in idea, advanced in technique and low in energy consumption and investment, and the system can run stably and is convenient to maintain.