On the basis of imaging principle of a coaxial spherical surface optical system,a new measuring method using glass capillary for the the refractive index of micro-quantity liquid was introduced.The refractive index was obtained through measuring the focal position of a capillary filled with the liquid by a reading microscope,and doing a calculation with an analytic formula.The refractive indexes of four liquid mediums,water,ethanol,ethylene glycol and glycerin were measured,the required sample was less than 0.002 ml,the precisions of obtained refractive indexes were better than 0.000 3 for water and ethanol,and 0.000 7 for ethylene glycol and glycerin.The results show that the new measuring method can be characterized by a micro-quantity sample,and has advantages in simple equipment,easy operation and high measurement accuracy.It is adapted to measure the refractive index of transparent or translucent micro-quantity liquid sample.