This paper mainly reports the extrapolation chamber for electron or Beta ray dosimetry with removable electrodes. It is equivalent to air, tissue and silicon. The diameters of the collecting electrode are 1.5 mm, 3 mm, 10 mm and 30 mm respectively. Convertible range is 0.2 mm-15 mm. It has the characteristics of measuring the internal temperature in ionization cavity, changing automatically the thickness of equivalent material layers above the chamber window and being controled by a microcomputer etc. It may be applied to measure the electron of no more than 10 MeV energy with a range of 10,5,-10,-3, Gy/h absorbed dose rate. The uncertainty of the whole system is 2.3% in measuring the surface dose rate of the ,204,Tl isotope Beta ray source. It is about 3.0% in measuring the depth absorbed dose rate of silicon and "Hami" melons for electron.