The diamond detector is used to diagnose X-ray and has the advantages of fast response, high sensitivity, large dynamic range, flat response, high breakdown field, and outstanding radiation hardness. The X-ray diamond detector with a metal-diamond-metal structur is developed, in which the optical grade diamond is synthesized by chemical vapor deposition (CVD) method. Through the calibration of response time on the pulse laser of 8 ps width, the full width at half maximum of the CVD diamond detector is 444 ps, the rise time of the detector is 175 ps, and the lifetime of the carrier is 285 ps. The detectors are used to measure the hard X-ray for the imploding experiment on SGIII-prototype equipment. The results indicate that the measured hard X-ray flux is produced mainly by laser and target imploding, and the peak signal is in direct proportion to the laser energy and in inverse proportion to the CH thickness of target.