The invention belongs to a subway station tunnel portal formwork under an ultrahigh voltage line and a quick installation and construction method thereof. The subway station tunnel portal formwork is composed of multiple separated transverse formwork bodies and multiple separated vertical formwork bodies, and the separated transverse formwork bodies are transversely connected in series through bolts to form an upper transverse formwork of a subway station tunnel portal transverse beam; each separated transverse formwork body is composed of a bottom plate and two side plates located on the two sides of the bottom plate; and an insulating plate of an anti-electric shock safety device is arranged in the space formed between the ultrahigh voltage line and the upper end of a scaffold. According to the subway station tunnel portal formwork under the ultrahigh voltage line and the quick installation and construction method thereof, the problems existing in construction of the subway station tunnel portal formwork under the multiple influences of complex environments such as the ultrahigh voltage line and adjacent urban main roads can be solved, and the advantages that the method is simple, convenient to operate and practical, large hoisting equipment is not needed, the construction speed is high, safety and reliability are achieved, the construction quality is good, the cost is low, and the using effect is good are achieved.