The invention provides a flexible circuit board, a mobile terminal and a mobile terminal fault detection method. The flexible circuit board comprises a first surface and a second surface, wherein the first surface and the second surface are opposite to each other. An LED light bar is arranged on the first surface. An antenna is arranged on the second surface. The flexible circuit board is integrated with the function of the antenna, which has the advantages of compact structure and space saving, is conducive to the thinning trend of electronic equipment, and is feasible for the practical application of the function of the antenna. The inconvenience of accessing an external antenna is avoided. The cost is saved. The user experience is improved.