A prototype of x-ray photon counting detector is proposed for x-ray pulsar navigation. The detector consists of CsI photocathode, micro-channel plate (MCP) electron multiplier, collect anode and electronic readout. The sensitivity, the temporal resolution, and the dead time are tested, and the results show that the sensitivity of the detector is 5.2× 103 A/W at 5 keV, the temporal resolution is 1.1 ns, and dead time is 100 ns.