The invention discloses an accurate radiotherapy planning system, comprising a CT data input module, a machine data module, a radiotherapy planning database, a target positioning module, a dosage computation module, a computer, an on-line dosage inversion module, a dosage collection module, a beam setting and preset ideal dosage distribution module, a setting beam module, a calculating beam dosage response matrix and determining beam intensity distribution module, a first determination module, a first evaluation result module, a calculating beam generated dosage and optimization module, a second evaluation result module, a second determination module and an output module. The accurate radiotherapy planning system has the characteristics of reasonable design and simple structure, and can accurately and rapidly calculate a target dosage, and substantially increase radiotherapy efficiency; in addition, an evaluation system makes dosages more accurate, is suitable for clinical usage, improves radiotherapy effects and reduces patient treatment pains.