The invention provides a bio-organic fertilizer employing pig dung as a raw material and a preparation method therefor. The bio-organic fertilizer comprises the following steps: firstly, pig dung is pretreated, and then chicken manure, fermentation agents and deodorizing fungicides are added; the C/N ratio is adjusted to 25-30:1 by utilization of urea or ammonium sulfate, the pH value is adjusted to 5.5-8.5 by utilization of calcium superphosphate the moisture content is kept at 50-60%, the materials are subjected to fermentation decomposition and then are crushed and sieved and then functional microbial agents are added; secondly, fermentation is carried out by utilization of compost fermentation. The beneficial effects are that firstly, the prepared bio-organic fertilizer raises output and economic benefits of crops of watermelons, bananas and the like greatly; the prepared bio-organic fertilizer improves physical, chemical and biologic properties of soil effectively; the agricultural product quality is raised; fourthly, development of agriculture and animal husbandry circular economy is promoted.