Abstract: Before bringing into production of dual horizontal wells by steam assisted gravity drainage (SAGD) process, the reservoir preheating between up an down parallel injection?production well pair is required. The preheating effectiveness is very important to the successful development by the SAGD process. In this paper, the calculation models for circulation preheating of dual horizontal wells by SAGD are developed. Taking one SAGD well pair in Fengcheng oilfield as an example, the relevant parameters during the preheating phase are simulated and calculated, including studies of the effects of distance between the two wells, the speed of steam circulation and the steam quality on the preheating effectiveness. The analysis indicates that when the steam quality in the phase of circulation preheating is 0.8, the speed of steam circulation should not be less than 30 t/d; while the speed reaches 60 t/d, the steam quality should not be less than 0.4; the distancebetween the horizontal well pair is about 5 m, the time of circulation preheating is about 93 days