Since the concept of X-ray communication was introduced, there is a great deal of research on the core components, such as X-ray source, receiving antenna and X-ray detectors. However, few people focus on the theoretical basis. Therefore, this paper aims at establishing a primary theoretical model of X-ray communication. At start, the power transmission process that to establish the link power equation was analysed. In addition, bit error ratio model based on Poisson distribution was established by analysing major noise sources. After that, the core parameters of X-ray communication, such as transmitting speed, communication distance, bit error ratio can be decided by a giving transmission power. Finally, in order to verify the bit error ratio model and link power equation, the signal photons of micro channel plate detector output under various X-ray anode voltage and modulations was testified. Experimental results accorded well with the theoretical analysis, OOK and 4-PPM modulation model can achieve 10-4 to 10-5 bit error ratio level. These models would improved the transmission theory and laid foundations for the application of future spatial X-ray communication to some extent.