The invention provides a calibration method of a position relationship between a welding robot and a position changer, which is characterized in that an oblique axis of the position changer is defined as a Z axis, and a rotating axis of the position changer is defined as a Y axis, an original point of a coordinate system is a crossing point O of a rotating axis line and a oblique axis line, and another axis which is vertical to the Z axis and conforms to right-hand rules is an X axis. The calibration method comprises the following steps of: enabling the position changer to respectively rotate to a plurality of positions around the rotating axis and the oblique axis through a robot controller, recording the position data of a TCP (Transport Control Protocol) point at the corresponding positions, establishing a spherical equation and fitting an optimal spherical surface based on a least square method to obtain the original point of the coordinate system of the position changer; and then enabling the TCP point to carry out multi-point marking in the two axial directions of the position changer by adopting a same method and further obtaining the direction vector of each coordinate axis based on a vector cross product method to realize the calibration of the position relationship. The calibration method has the benefit that in order to eliminate the effect of accidental factors, a distance deviation rate concept and a set point threshold value determination method are proposed, so that the calibration precision is improved.