The invention discloses a continuous adjustable piston height type self-locking energy-saving engine. The engine comprises an engine system and a piston adjusting system, wherein the engine system comprises a cylinder cover, an electric oil injector, a cylinder body, a main piston, a connecting rod, a crankshaft and an engine oil pump, wherein the piston adjusting system comprises a secondary piston, a self-locking solenoid valve, a returning solenoid valve, a returning spring, a controller, a pressure sensor and a temperature sensor; the secondary piston, the returning solenoid valve and thereturning spring are sleeved with the main piston; the self-locking solenoid valve is connected to the cylindrical sidewall between the main piston and the secondary piston; and an oil inlet and an oil outlet are formed in the lower part of the main piston. The engine is simple in structure; the adjusting method is simple, easy and reliable; the requirements on the discharge, compressing ratio, inner pressure of a cylinder and temperature in the cylinder of the engine under different rotating speed and different load can be met in real time; the applicable scope is wide; and the good economicbenefits and the emission reduction effect are achieved after popularization.