The invention relates to a portable device based on a smart phone measurement spectrum and a spectral detection method thereof and belongs to the technical field of spectral detection and image processing. The portable device for measuring the spectrum by utilizing the smart phone mainly comprises an incident slit, a collimating lens, a grating, a cylindrical mirror, a standard white board, a packaging clamp and a smart phone. A target light source is dispersed through the slit, the lens and the grating, imaging is carried out on the standard white board, and a shot image is processed at the phone end to obtain a target spectrum, wherein the adaptation of the device and different mobile phones can be realized according to the novel micro optical peripheral accessory and the image processing method, thereby avoiding the limitation that measurement cannot be carried out when the optical device is not matched with the mobile phone camera in the prior art. Compared with the traditional portable spectrometer, a smart phone is used for replacing a CCD or CMOS sensor so as to achieve lower cost, convenient carrying and convenient data transmission are achieved through a novel method for separating the optical device and the image processing device.