Abstract: L oilfield is the first cyclic steam stimulation(CSS) pilot in Bohai bay. Accurate evaluation of the dynamics and performance of CSS helps to guide and promote the following CSS development technology. The status of injection, bottom hole temperature, oil flow rate, water cut, and incremental oil under thermal recovery of L oil field were analyzed based on CSS well dynamics. The bottom hole temperature after CSS reached103℃, and then decreased rapidly. The bottom hole temperature obtained from CSS is higher than multithermal fluid stimulation. According to the production rate, CSS production process can be subdivided into four phases: water production phase, peak oil production phase, fast decline phase, and low stabilized oil production phase. The production decline trend follows exponential decline. The first-round monthly decline rate is 22.3%～28.6%. The first month average production rate is as 2.5 to 2.8 times of production under pressure depletion only. The first-year average daily production or the annual production under CSS is 0.7 to1.2 times higher compared with pressure depletion, with an average of 2.0. CSS can obviously increase the development effect of Bohai heavy oilfield.