Abstract: The new power system has reshaped the structure of energy production and consumption, and the electricity market mechanism also needs to change accordingly. First, this paper points out that the improvement of system flexible adjustment capability is the primary goal of the market mechanism design for the new power system. Characteristics of the market mechanism that can achieve this goal are given, including stimulating the adjustment motivation, unleashing the adjustment capability, and accommodating various new flexible resources. Then, the time-of-use trading mechanism that is generally adopted in the spot markets of various countries in the world is analyzed and its many incompatibilities with the new power system are pointed out, including that the adjustment capability contribution of market entities cannot be quantified and represented, the continuous operation characteristics of market entities are inconsistent with the time-of-use trading mechanism, resulting in difficulty in fully unleashing the potential adjustment capability, and it is difficult to meet the demand for massive direct participation of flexible resources in the electricity market. Therefore, this paper abandons the method of time-of-use trading and instead proposes the concept of holistic trading mechanism and substitute power product. The main ideas for forming and trading substitute power products are introduced, and a new market mechanism is conceived with the substitute power product as the core. This mechanism can quantify the adjustment contribution of market entities by assigning the adjustment responsibilities, and stimulate the adjustment motivation of market entities. Meanwhile, it can also promote the market entities to actively optimize their own operation methods and unleash adjustment capabilities. Furthermore, it has the advantage of being easy to expand and can easily accommodate various new market entities in the new power system.