This paper presents an efficient and stable algorithm to intra-operative planning for prostate brachytherapy. As a heuristic approach, the algorithm selects one seed at a step and iterates until predefined prostate volume is covered by prescribed dose. For each step, potential seeds are evaluated according to the ability to irradiate the target while sparing adjacent organs at risk. And its influence on dose homogeneity is also taken into account. Furthermore, a flexible mechanism is adopted to limit the number of used needles. The mechanism selects acceptable sub-optimal seed in existing needles instead of optimal seed that requires adding a new needle. The efficacy of algorithm is evaluated on five clinical cases. Compared with state-of-the-art methods,this algorithm is efficient and stable without the trial and error process of determining various parameters. These advantages make the algorithm suitable for intra-operative real-time treatment planning. As a heuristic approach, the algorithm selects one seed at a step and iterates until predefined prostate volume is covered by prescribed dose. Each paper for an efficient and stable algorithm to intra-operative planning for prostate brachytherapy. according to the ability to irradiate the target while sparing adjacent organs at risk. And its influence on dose homogeneity is also taken into account. And, a flexible mechanism is adopted to limit the number of used needles. in existing needles instead of optimal seed that requires adding a new needle. Compared with state-of-the-art methods, this algorithm is efficient and stable without the trial and error process of determining various parameters. These advantages make the algorithm suitable for intra-operative real-time treatment planning.