The invention relates to the field of electronic detection, in particular to a device for detecting the flatness of an electronic component. The device comprises a walking unit and a detecting unit. The walking unit comprises a first walking frame and a second walking frame. The detecting unit is arranged on the first walking frame and comprises a fixing plate fixed to the first walking frame. Thefixing plate is hinged to a detecting rod. The lower end of the detecting rod is provided with a detecting mechanism. The upper end of the detecting rod is connected with a marking mechanism. A resetting component is connected between the detecting rod and the fixing plate. The detecting mechanism comprises a detecting cylinder. A detecting pen and a marking pen are slidably connected in the detecting cylinder. The end portion of the detecting pen is connected to the detecting rod. One end of the marking pen is opposite to the detecting rod. The marking mechanism comprises a marking cylinderfixed to the fixing plate. The upper end of the marking cylinder is in sealed connection with a piston plate. A piston rod is connected between the piston plate and the detecting rod. A marking hole is arranged at the bottom of the marking cylinder. The device can achieve a purpose of detecting the flatness of the corners of the electronic component.