The invention discloses a fast and accurate measurement method for the sectional area of a cable conductor or an insulating layer, which comprises the steps of S1, selecting a cable to be tested withthe length being L, and putting the selected cable in a preset sealed measurement container; S2, pushing a piston of the sealed measurement container to a first scale value V1 for standing, and recording a first air pressure value P1 displayed by an air pressure gauge; S3, pushing the piston of the sealed measurement container to an ith scale value Vi for the ith standing, and recording a displayed ith air pressure value Pi after the air pressure indication is stable; and S4, calculating the sectional area of the cable to be tested according to the data recorded in the step S2 and the step S3.The fast and accurate measurement method obtains the technical effects that the variation of the pressure intensity in the container before and after the change is measured through changing the volume of the sealed measurement container loaded with the tested piece, the volume of the tested piece is calculated, and thus the sectional area of the tested piece is solved. The container does not needto be vacuumized during the testing process, and there is no influence of factors such as the vacuum degree and bubbles in the tested piece, so that the measurement is enabled to be more convenient and more efficient.