The invention relates to a constant-current charging circuit based on a simple switching voltage source. The constant-current charging circuit at least comprises a constant-current source (2) and a switching power supply (1), wherein the switching power supply (1) converts an alternating voltage into a required direct voltage; the constant-current source controls the output voltage of the switching power supply, and supplies a required constant-current charging current to a charging battery; the constant-current charging circuit is characterized in that the constant-current source (2) and the charging battery (4) are connected with the output end of the switching power supply in series; and the charging battery (4) is connected with a constant-voltage circuit (3) in parallel. The constant-current charging circuit has the characteristics of stable performance, low cost and the like.