Abstract: Under the natural circulation conditions, the CHF occurring in rectangular channels is influenced by lots of factors, which have not understood completely yet. The experimental results obtained from current research were compared with the calculation results of Katto forced circulation model and Zhang natural circulation model. The applicability of the two models and effects of inlet velocity, outlet quality and pressure on the CHF under the experimental conditions were analyzed. Research indicated that the calculation results of Zhang model coincided better with the experimental values than that of Katto model. As the inlet velocity increased, the CHF of both natural and forced circulations would increase. As the outlet quality increased, the CHF of both circulations would decrease. As the system pressure increased, the CHF of both circulations would increase, and the increment speed of CHF would decrease under the higher pressure condition in natural circulation.