根据官方文档：

Gas

One important aspect of the way the EVM works is that every single operation that is executed inside the EVM is actually simultaneously executed by every full node. This is a necessary component of the Ethereum 1.0 consensus model, and has the benefit that any contract on the EVM can call any other contract at almost zero cost, but also has the drawback that computational steps on the EVM are very expensive. Roughly, a good heuristic to use is that you will not be able to do anything on the EVM that you cannot do on a smartphone from 1999. Acceptable uses of the EVM include running business logic (“if this then that”) and verifying signatures and other cryptographic objects; at the upper limit of this are applications that verify parts of other blockchains (eg. a decentralized ether-to-bitcoin exchange); unacceptable uses include using the EVM as a file storage, email or text messaging system, anything to do with graphical interfaces, and applications best suited for cloud computing like genetic algorithms, graph analysis or machine learning.

In order to prevent deliberate attacks and abuse, the Ethereum protocol charges a fee per computational step. The fee is market-based, though mandatory in practice; a floating limit on the number of operations that can be contained in a block forces even miners who can afford to include transactions at close to no cost to charge a fee commensurate with the cost of the transaction to the entire network; see the whitepaper section on fees for more details on the economic underpinnings of our fee and block operation limit system.