Objective To optimize pulse parameters in order to prepare the composite coating with high microhardness. Methods Ni-nano Al2O3 composite coatings were prepared by pulse electroplating under ultrasound condition, and the influences of average current density, duty cycle, frequency and electroplating time on the microhardness were also investigated. Results The microhardness of Ni-nano Al2O3 composite coatings increased first and then decreased with the increase of average current density, duty cycle and frequency, and it tended to decrease approximately with the electroplating time prolonging. Conclusion The Ni-nano Al2O3 composite coating prepared under the condition of average current density 8 A/ dm2, duty cycle 0. 6, frequency 1. 5 kHz and electroplating time 3 min had the highest microhardness of about 427. 1HV. It was concluded that nano Al2O3 particles of high composite quantity had effects of dispersion strengthening and grain refinement strengthening and improved the density of composite coating structure, thus improving microhardness.