The invention discloses a high-sensitivity method for detecting lattice distortion in a single bent semiconductor nanowire based on second harmonic generation microscopy. Under a microscopic system, a single nanowire is pushed by the use of a probe to bend the end so as to generate different degrees of lattice distortion. Simultaneously, a laser beam is focused onto one point A on the single nanowire, included angle (polarizing angle Theta) between polarization direction of pump light and long axis of the nanowire is continuously changed, and changing relation of second harmonic intensity with the polarizing angle Theta is determined. With the focusing position of pump light at the A point unchanged and with gradually increasing of bending curvature, ratio of second harmonic intensities when the polarizing angle Theta equals to 90 degrees and 0 degree is remarkably reduced. The invention provides a novel all-optical method for determining lattice distortion of a semiconductor nanowire. In comparison with traditional transmission electron microscopy, the invention has advantages as follows: detection sensitivity is raised by near an order of magnitude; samples are not damaged; bulk materials can be detected; and the method of the invention is applicable to various environments of liquid state, low temperature and the like.