Cylinder ferrite magnetic core is a batch of black cylindrical samples and its crack contrast is low. The crack imaging result of traditional machine vision is not good. Laser infrared thermography detection technology relies on the sample surface temperature distribution to detect the crack defects, which solve the problem of low contrast micro crack detection. When the crack is detected by line laser or point laser, the cracks parallel to the laser scanning direction is hard to detect because of the small heat flow on both sides. Dual linear array laser thermography system with dislocation arrangement creates multi-direction heat flow, which can detect arbitrary direction cracks. In order to verify the feasibility of dual linear array laser to detect arbitrary direction cracks, simulation took the laser scanning process of 0°, 45° and 90° cracks. Linear array laser had great non-uniformity in the power distribution of each spot, so different parameter design had great influence on crack detection. Therefore, the design parameters such as spot radius, spot center distance, linear array laser dislocation distance, linear array laser distance, and motion velocity were optimized to improve the SNR in crack detection. Crack imaging algorithm generated cracks based on temperature spatial gradient. Due to the non-uniformity of the laser spots, the gradient of the crack at different relative positions between two laser beams was different. Algorithm selected the position of the cracks with large relative gradient between two laser beams. Through the fusion of multiple gradient images, crack imaging algorithm achieved arbitrary direction crack detection. The imaging algorithm was designed according to the crack spatial temperature gradient characteristics excited by dual linear array laser. Four cylinder ferrite samples with horizontal, vertical and inclined natural cracks were tested, and the imaging results showed all the cracks clearly and intuitively.