Abstract: The pool boiling characteristic of vertical tube bundle was investigated by controlling the steam parameters in vertical tubes immersed in head water tank. Through the comparison of wall superheat and various condensate flow rate, the difference of boiling heat transfer coefficient between central tube and side tube was analyzed. The experimental results show that the boiling heat transfer coefficient of tube bundle is significantly better than that of single tube, which is about 1.2-1.5 times of single tube under the condition of same heat flux. Compared with side tube, the heat transfer capability of center tube is superior in low thermal load condition, while the performance of center tube is inferior in high thermal load condition. When heat flux is higher than 200 kW/m², the boiling heat transfer coefficient of side tube increases about 7% with respect to that of center tube, which will be further expanded gradually with the increase of heat flux according to the trend of experimental data.