Blood sampling pen convenient for assembling

The invention discloses a blood sampling pen convenient for assembling. An ejection device is installed in a pen body and includes an ejection rod, a clamping sleeve clamped on the tail end of the ejection rod, and an ejection cavity sleeving the outside of the ejection rod; the tail end of the ejection rod is bifurcated to form upper and lower clamping strips which have elastic gaps in the middleparts; the tail ends of the clamping strips or the inner wall of the clamping sleeve is arranged into a double-breasted structure; and the outer wall of the ejection cavity or the inner wall of the pen body is arranged into the double-breasted structure. During assembling, a sleeving member can be limited between two clamping bulges with slight force application, so that pre-clamp connection canbe realized, scattering and escaping cannot happen with random placing in process flow, and therefore, assemblers can conveniently perform installation; and force is applied to push and press, so thatthe ejection rod and the c