A lighting device installation method includes the following steps. Firstly, a holder including a first stopping structure and a first engaging structure is fixed on an installation surface. Then, a lighting device including a second stopping structure and a third stopping structure is provided. The second stopping structure and the third stopping structure are collaboratively defined as a second engaging structure. Then, the second engaging structure of the lighting device is stopped by the first stopping structure of the holder, so that the lighting device is supported by the lower portion of the holder. Then, electrical connection between the lighting device and a power source is established. Afterwards, the second engaging structure of the lighting device is engaged with the first engaging structure of the holder, so that the lighting device is supported by the upper portion of the holder.