The invention discloses an optical fiber-coupled laser sum frequency technology-based trace mercury concentration detection method and device. The device comprises a data acquisition card, two laser diode drivers, two diode lasers with tail fibers and different wavelengths, a 1: 2 tapering lens optical fiber, barium metaborate (BBO) crystals, a quartz lens, a beam splitter prism, two reflectors, a light splitter, a reference cell, a sample tank, two photomultipliers, two filters and a computer. The method utilizes a multiple linear regression algorithm and an automatic circuit control wavelength feedback technology to realize on-line continuous detection of a mercury vapor concentration.