Polysiloxane is an ideal material for the preparation of wearable and flexible electronic devices. The preparation of pressure sensor using polysiloxane with both self-healing properties and excellent mechanical properties remains a key challenge. This work reports a self-healable pressure sensor based on polysiloxane network cross-linked by dynamic Diels-Alder bonds. The self-healable polysiloxane underwent a solid-liquid-solid transformation during a self-healing process, which has been confirmed by rheology. Depending on the amount of the linear reactive polydimethylsiloxane, mechanical performance and stretchability of the self-healable polysiloxane were tunable. By incorporating graphene nanosheets into polysiloxane elastomer, we fabricated a self-healable nanocomposite with significantly improved tensile stress and excellent electromechanical property. The tensile stress of nanocomposite containing 35wt% graphene was 1.09MPa that was improved by more than 1700% compared to that of the elastomer, indicating a significant improvement of the tensile stress with stretchability. The prepared self-healable pressure sensor exhibits a high sensitivity of 0.765kPa(-1) and a gauge factor of 4.87, demonstrating a promising potential use in the pressure sensors.