Almost no existing robots can move across mud and swim in water. Our proposed heter-stiffness robot consists of a rigid spiral forepart and a soft helical tail. The rigid head moves better in a high viscosity solution, while the soft tail moves well in a dilute solution, demonstrating high environmental adaptability with a wide viscosity range. The proposed robot can also adapt to energy distribution to achieve more efficient motion. The miniature robot can move bi-directionally, allowing it to avoid obstacles under wireless control to achieve underwater detection/sample collection missions.