Games like 仙之气
Games like 仙之气 include Terraria, Graveyard Keeper, Stardew Valley, 鬼谷八荒 Tale of Immortal, and People Playground. We matched them by the tags players give 仙之气 on Steam (Exploration, Simulation, Pixel Graphics, Sandbox, and Building): closest matches first, and among equally close ones the better-known games.

Terraria
Shared: Sandbox · Pixel Graphics · Exploration

Graveyard Keeper
Shared: Pixel Graphics · Simulation · Sandbox

Stardew Valley
Shared: Pixel Graphics · Simulation · Sandbox

鬼谷八荒 Tale of Immortal
Shared: Simulation · Sandbox · Singleplayer

People Playground
Shared: Sandbox · Simulation · Singleplayer

Core Keeper
Shared: Exploration · Pixel Graphics · Sandbox

The Escapists
Shared: Pixel Graphics · Simulation · Singleplayer

Kerbal Space Program
Shared: Simulation · Sandbox · Building

Cities: Skylines
Shared: Simulation · Building · Sandbox

Spaceflight Simulator
Shared: Sandbox · Simulation · Exploration

The Scroll of Taiwu : Beyond The Dome
Shared: Sandbox · Simulation · Singleplayer

Oxygen Not Included
Shared: Building · Singleplayer · Simulation

DAVE THE DIVER
Shared: Pixel Graphics · Exploration · Singleplayer

Prison Architect
Shared: Simulation · Sandbox · Building

觅长生
Shared: Turn-Based Combat · Simulation · Strategy

WorldBox - God Simulator
Shared: Simulation · Sandbox · Pixel Graphics

Cities: Skylines II
Shared: Simulation · Sandbox · Building

Totally Accurate Battle Simulator
Shared: Simulation · Sandbox · Singleplayer

Monster Sanctuary
Shared: Pixel Graphics · Exploration · Turn-Based Combat

Papers, Please
Shared: Simulation · Pixel Graphics · Indie

Space Engineers
Shared: Sandbox · Simulation · Building

Forager
Shared: Pixel Graphics · Sandbox · Indie

Automation - The Car Company Tycoon Game
Shared: Simulation · Sandbox · Building

Planet Coaster
Shared: Simulation · Building · Sandbox