The invention relates to a magnesium alloy surface nanometer chemical complex plating solution and the preparing process and application thereof. The complex plating solution comprises basic chemical plating solution and nanometer oxide concentrates, the nanometer oxide concentrates is added into the basic chemical plating solution, the complex plating solution is dispersed for 5 to 30 minutes under 40-100KHz ultrasonic, and stood for 2 to 5 hours. The chemical platingis divided into the following two steps: plating is carried out for 5 to 30 minutes in the basic chemical plating solution without nanometer powder to fully coat the matrix by a nickel layer; and then plating is carried out in the complex plating solution with nanometer powder, the complex plating solution is mixed intermittently by ultrasonic with a frequency of 50 to 80 KHz to make the nanometer powder always in a good dispersion state in the complex plating solution, the temperature is controlled between 70 DEG C to 90 DEG C, the time lasts for 1 to 3 hours. According to the invention, the nanometer oxide is added into the plating solution in nanometer concentrates form, the concentrates has good dispersivity, high solid content good stability, and can be stored for more than half a year. The nanometer powder in the plating layer has high and uniform compound quantity, high hardness, good corrosion resistance and wearing resistance.