Due to tool cutting position changing during milling process, output error is brought to fixed milling dynamometer. A fixed three components dynamometer with stain gauges bounded on four vertical sensitive beams is proposed to reduce the influence of milling position variation. Within the milling rang limit, the output error of the developed sensor is kept in an acceptable range. Static force applied test and dynamic milling experiment are both implemented. In a static force test with force applied on the 70mm×70mm×15mm workpiece,the maximum decoupling deviation is 5.58%. In milling experiment with identical machining parameters but different milling positions, the differences of peak to peak force values derived from sensor output are not more than 3.73%. The research on the dynamometer provides a new thought and reference to decoupling issues for strain based fixed milling force sensor with high stiffness in vertical direction.