This study aims to integrate the ‘Crab-Grass-Snail’ system and the ‘Cultivating-Purifying’ system into a more comprehensive recycling ecosystem, and theoretically investigate the engineering practice to meet the Ⅲ type surface water standard. Through constructing a system dynamic model, this study simulated the optimal area ratio between crab cultivation pond and purification pond, as well as testing the effects of feed substitution ratio, water quality regulation technology and purifying efficiency on TN and TP concentration. The simulation results showed that the optimal area ratio for cultivation pond and purification pond was 20.5 to meet the Ⅲ type surface water standard. It was reduced by 3.1%, 6.3% and 10.0% for TN concentration and by 4.2%, 8.3% and 8.3% for TP concentration in the cultivation pond with a substitution of commercial feeds for 5%, 10% and 15%, respectively. TN concentration was decreased by 4.5%, 10.1% and 14.6% in the purification pond with a substitution of commercial feeds for 5%, 10% and 15%, respectively. Water quality regulation technology did not affect TN and TP concentration in the cultivation and purification ponds. Compared with one time's harvest for water hyacinth, it was reduced 10.0% and 10.0% for TN concentration and 11.1% and 11.1% for TP concentration in the cultivation pond by harvest two times and three times, respectively. TN concentration was decreased by 16.1% and 17.2% in the purification pond. In summary, N and P input from commercial feeds were an important cause for the over-range of N and P concentration in the residue water. TN and TP concentration will decrease with increasing substitution rate for commercial feeds in the cultivation and purification ponds. It needs only to harvest two times for water hyacinth when the purifying water will meet the Ⅲ type surface water standard. These results will provide theoretical evidence for engineering design and the mating management practice for the crab ecological cultivation.