Encapsulating metal nanoparticles in carbon shells (Metal@C) to enhance catalytic activity and stability has been certified feasible. However, most existing methods for preparing Metal@C are complex, time-consuming, and lack of scalability. In this study, a novel method that couples the high-temperature shock (HTS) with ultrasonic spray pyrolysis is reported, which can realize facile and scalable production of various Metal@C through the pyrolysis of glucose and metal chloride mixtures. The proposed HTS ultrasonic spray pyrolysis offers several advantages, including compact size, short reaction time (~ 120 ms), and uniform heating. Taking the Ni@C-40 nanocomposite as an example, the ultrasmall Ni nanoparticles (~ 10 nm) with thin carbon protective shells (~ 2 nm) are uniformly dispersed in the carbon matrix and applied for oxygen evolution reaction (OER) in alkaline media. The Ni@C-40 optimized by tuning the thickness of carbon shell exhibits significantly enhanced OER activity with low overpotential of 242 mV at 10 mA·cm⁻² and stability, which is attributed to the optimized interactions between Ni nanoparticles and carbon shells. This method also shows promise for continuous pyrolysis synthesis of various extreme materials at ultra-high temperatures using alternative electric heating materials.