Unsteady cavitation is an important topic due to its potential to cause huge damage to the hydraulic machinery. To control the shedding of cloud cavitation, the cavitation over a flat hydrofoil with an obstacle is investigated experimentally and numerically. A series of experiments around the flat hydrofoil without/with obstacle are carried out to study the evolution of cavitation. Periodic re-entrant jet and large shedding of cloud cavitation are observed in the case without obstacle, while the shedding of cloud cavitation in the case with obstacle is much weaker. Numerical simulations of the 2D unsteady cavitating flows around the hydrofoil are also performed. The transient and averaged fields of numerical simulations are presented and compared with the experimental data. The results show that in cases without obstacle, the averaged cavity length becomes longer with the decrease of the cavitation number. While in cases with obstacle, there is a range of cavitation number, in which the averaged cavity length almost keeps constant. The existence of obstacle changes the strength and direction of the transient re-entrant jet as well as the pressure distribution at the tail part of the cavity, leading to the weaker shedding of the cloud cavitation. •Period shedding and re-entrant jet are detected in the case with/without obstacle, while the shedding is much weaker in the case with obstacle.•The thickness and the length of the cavity in the case with obstacle both decrease apparently compared with the case without obstacle.•A peak can be found in the adverse pressure gradient distribution in the case without obstacle, while it decreases obviously in the case with obstacle.