The invention provides a construction method of a concrete pile. According to the construction method, at first, diameter expanding and varying concrete pile body construction is performed, and then, a pile end is installed, and pile-side post-casting is performed, and therefore, the bearing capacity of the pile can be greatly increased. The construction method includes the following steps that: 1) pile body pore-forming is performed at a pile position, diameter expanding is performed on a pile body or a pile bottom in squeezing expanding, rotating expanding and drilling expanding manners in pore-forming or after pore-forming; 2) a steel reinforcement cage with slurry-jacking pipes is immersed into a pile hole, slurry outlets are located at corresponding positions of the pile bottom and a diameter expanded portion respectively; 3) pile body concrete is poured into the pile hole; and 4) after the pile body concrete has a certain strength, cement slurry is injected into the slurry-jacking pipes through pressure, so that the cement slurry can diffuse and permeate to the lower part of the pile end and soil at the periphery of the pile body under the action of pressure, and will be solidified at the lower part of the pile end and the soil at the periphery of the pile body, and therefore, the strength of the soil at the periphery of the pile can be improved when the diameter of the pile is further increased.