The invention provides a large-tow PAN (polyacrylonitrile) base carbon fiber protofilament oil agent, which mainly solves the problem that in the prior art, the consumption of emulsifying agents in the oil agent used for the carbon fiber protofilament is high, so the heat resistance of the oil agent in the use process is poor. The large-tow PAN base carbon fiber protofilament oil agent is adopted and comprises the following ingredients through being metered in parts by weight: a, 5 to 20 parts of amino modified polydimethylsiloxane A; b, 40 to 60 parts of amino modified polydimethylsiloxane B; c, 10 to 30 parts of polyether modified polydimethylsiloxane; and d, 5 to 20 parts of emulsifying agents. Through the technical scheme, the problem is perfectly solved, and the large-tow PAN base carbon fiber protofilament oil agent can be used for the industrial production of large-tow PAN base carbon fiber protofilaments.