Photon spiking neurons are connected by weighting devices, so the implementation of weighting devices is critical for realizing the large-scale computation of neural networks. Based on the variable optical attenuator (VOA), a weighting device for automatically adjusting photon spiking neuron is developed. The weighting device includes VOA, photoelectric detector, single chip, analog to digital converter, digital to analog converter, amplification module, etc. The weighting device can quickly calculate and look up table, and the attenuation values of VOA can be adjusted online based on the received optical signal. The weighting device has the advantages of high efficiency and easy implementation. When we combine the optical spike-timing-dependent plasticity (STDP) circuits and the proposed weighting device, STDP learning mechanisms for photon spiking neural can be achieved. The weighting device is detected when the height of STDP curve window is 0.2, and four STDP learning curves are obtained. The experimental results are consistent with the theoretical computation results.